StringUtilsTest.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3;

import static org.apache.commons.lang3.LangAssertions.assertIllegalArgumentException;
import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertNotEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertSame;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.UnsupportedEncodingException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Objects;
import java.util.function.Supplier;
import java.util.regex.PatternSyntaxException;

import org.apache.commons.lang3.function.Suppliers;
import org.apache.commons.lang3.mutable.MutableInt;
import org.apache.commons.lang3.text.WordUtils;
import org.junit.jupiter.api.Disabled;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvSource;
import org.junit.jupiter.params.provider.ValueSource;
import org.junitpioneer.jupiter.DefaultLocale;
import org.junitpioneer.jupiter.ReadsDefaultLocale;
import org.junitpioneer.jupiter.WritesDefaultLocale;

/**
 * Tests for methods of {@link StringUtils}
 * which been moved to their own test classes.
 */
@SuppressWarnings("deprecation") // deliberate use of deprecated code
class StringUtilsTest extends AbstractLangTest {

    static final String WHITESPACE;
    static final String NON_WHITESPACE;
    static final String HARD_SPACE;
    static final String TRIMMABLE;
    static final String NON_TRIMMABLE;

    static {
        final StringBuilder ws = new StringBuilder();
        final StringBuilder nws = new StringBuilder();
        final String hs = String.valueOf((char) 160);
        final StringBuilder tr = new StringBuilder();
        final StringBuilder ntr = new StringBuilder();
        for (int i = 0; i < Character.MAX_VALUE; i++) {
            if (Character.isWhitespace((char) i)) {
                ws.append((char) i);
                if (i > 32) {
                    ntr.append((char) i);
                }
            } else if (i < 40) {
                nws.append((char) i);
            }
        }
        for (int i = 0; i <= 32; i++) {
            tr.append((char) i);
        }
        WHITESPACE = ws.toString();
        NON_WHITESPACE = nws.toString();
        HARD_SPACE = hs;
        TRIMMABLE = tr.toString();
        NON_TRIMMABLE = ntr.toString();
    }

    private static final String[] ARRAY_LIST = {"foo", "bar", "baz"};
    private static final String[] EMPTY_ARRAY_LIST = {};
    private static final String[] NULL_ARRAY_LIST = {null};
    private static final Object[] NULL_TO_STRING_LIST = {
            new Object() {
                @Override
                public String toString() {
                    return null;
                }
            }
    };
    private static final String[] MIXED_ARRAY_LIST = {null, "", "foo"};
    private static final Object[] MIXED_TYPE_LIST = {"foo", Long.valueOf(2L)};
    private static final long[] LONG_PRIM_LIST = {1, 2};
    private static final int[] INT_PRIM_LIST = {1, 2};
    private static final byte[] BYTE_PRIM_LIST = {1, 2};
    private static final short[] SHORT_PRIM_LIST = {1, 2};
    private static final char[] CHAR_PRIM_LIST = {'1', '2'};
    private static final float[] FLOAT_PRIM_LIST = {1, 2};
    private static final double[] DOUBLE_PRIM_LIST = {1, 2};
    private static final List<String> MIXED_STRING_LIST = Arrays.asList(null, "", "foo");
    private static final List<Object> MIXED_TYPE_OBJECT_LIST = Arrays.<Object>asList("foo", Long.valueOf(2L));
    private static final List<String> STRING_LIST = Arrays.asList("foo", "bar", "baz");
    private static final List<String> EMPTY_STRING_LIST = Collections.emptyList();
    private static final List<String> NULL_STRING_LIST = Collections.singletonList(null);

    private static final String SEPARATOR = ",";
    private static final char SEPARATOR_CHAR = ';';
    private static final char COMMA_SEPARATOR_CHAR = ',';

    private static final String TEXT_LIST = "foo,bar,baz";
    private static final String TEXT_LIST_CHAR = "foo;bar;baz";
    private static final String TEXT_LIST_NOSEP = "foobarbaz";

    private static final String FOO_UNCAP = "foo";
    private static final String FOO_CAP = "Foo";

    private static final String SENTENCE_UNCAP = "foo bar baz";
    private static final String SENTENCE_CAP = "Foo Bar Baz";

    private static final boolean[] EMPTY = {};
    private static final boolean[] ARRAY_FALSE_FALSE = {false, false};
    private static final boolean[] ARRAY_FALSE_TRUE = {false, true};
    private static final boolean[] ARRAY_FALSE_TRUE_FALSE = {false, true, false};

    private void innerTestSplit(final char separator, final String sepStr, final char noMatch) {
        final String msg = "Failed on separator hex(" + Integer.toHexString(separator) +
                "), noMatch hex(" + Integer.toHexString(noMatch) + "), sepStr(" + sepStr + ")";

        final String str = "a" + separator + "b" + separator + separator + noMatch + "c";
        String[] res;
        // (str, sepStr)
        res = StringUtils.split(str, sepStr);
        assertEquals(3, res.length, msg);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals(noMatch + "c", res[2]);

        final String str2 = separator + "a" + separator;
        res = StringUtils.split(str2, sepStr);
        assertEquals(1, res.length, msg);
        assertEquals("a", res[0], msg);

        res = StringUtils.split(str, sepStr, -1);
        assertEquals(3, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals("b", res[1], msg);
        assertEquals(noMatch + "c", res[2], msg);

        res = StringUtils.split(str, sepStr, 0);
        assertEquals(3, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals("b", res[1], msg);
        assertEquals(noMatch + "c", res[2], msg);

        res = StringUtils.split(str, sepStr, 1);
        assertEquals(1, res.length, msg);
        assertEquals(str, res[0], msg);

        res = StringUtils.split(str, sepStr, 2);
        assertEquals(2, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals(str.substring(2), res[1], msg);
    }

    private void innerTestSplitPreserveAllTokens(final char separator, final String sepStr, final char noMatch) {
        final String msg = "Failed on separator hex(" + Integer.toHexString(separator) +
                "), noMatch hex(" + Integer.toHexString(noMatch) + "), sepStr(" + sepStr + ")";

        final String str = "a" + separator + "b" + separator + separator + noMatch + "c";
        String[] res;
        // (str, sepStr)
        res = StringUtils.splitPreserveAllTokens(str, sepStr);
        assertEquals(4, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals("b", res[1], msg);
        assertEquals("", res[2], msg);
        assertEquals(noMatch + "c", res[3], msg);

        final String str2 = separator + "a" + separator;
        res = StringUtils.splitPreserveAllTokens(str2, sepStr);
        assertEquals(3, res.length, msg);
        assertEquals("", res[0], msg);
        assertEquals("a", res[1], msg);
        assertEquals("", res[2], msg);

        res = StringUtils.splitPreserveAllTokens(str, sepStr, -1);
        assertEquals(4, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals("b", res[1], msg);
        assertEquals("", res[2], msg);
        assertEquals(noMatch + "c", res[3], msg);

        res = StringUtils.splitPreserveAllTokens(str, sepStr, 0);
        assertEquals(4, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals("b", res[1], msg);
        assertEquals("", res[2], msg);
        assertEquals(noMatch + "c", res[3], msg);

        res = StringUtils.splitPreserveAllTokens(str, sepStr, 1);
        assertEquals(1, res.length, msg);
        assertEquals(str, res[0], msg);

        res = StringUtils.splitPreserveAllTokens(str, sepStr, 2);
        assertEquals(2, res.length, msg);
        assertEquals("a", res[0], msg);
        assertEquals(str.substring(2), res[1], msg);
    }

    /**
     * Tests {@code appendIfMissing}.
     */
    @Test
    void testAppendIfMissing() {
        assertNull(StringUtils.appendIfMissing(null, null), "appendIfMissing(null,null)");
        assertEquals("abc", StringUtils.appendIfMissing("abc", null), "appendIfMissing(abc,null)");
        assertEquals("xyz", StringUtils.appendIfMissing("", "xyz"), "appendIfMissing(\"\",xyz)");
        assertEquals("abcxyz", StringUtils.appendIfMissing("abc", "xyz"), "appendIfMissing(abc,xyz)");
        assertEquals("abcxyz", StringUtils.appendIfMissing("abcxyz", "xyz"), "appendIfMissing(abcxyz,xyz)");
        assertEquals("aXYZxyz", StringUtils.appendIfMissing("aXYZ", "xyz"), "appendIfMissing(aXYZ,xyz)");

        assertNull(StringUtils.appendIfMissing(null, null, (CharSequence[]) null), "appendIfMissing(null,null,null)");
        assertEquals("abc", StringUtils.appendIfMissing("abc", null, (CharSequence[]) null), "appendIfMissing(abc,null,null)");
        assertEquals("xyz", StringUtils.appendIfMissing("", "xyz", (CharSequence[]) null), "appendIfMissing(\"\",xyz,null))");
        assertEquals("abcxyz", StringUtils.appendIfMissing("abc", "xyz", (CharSequence) null), "appendIfMissing(abc,xyz,{null})");
        assertEquals("abc", StringUtils.appendIfMissing("abc", "xyz", ""), "appendIfMissing(abc,xyz,\"\")");
        assertEquals("abcxyz", StringUtils.appendIfMissing("abc", "xyz", "mno"), "appendIfMissing(abc,xyz,mno)");
        assertEquals("abcxyz", StringUtils.appendIfMissing("abcxyz", "xyz", "mno"), "appendIfMissing(abcxyz,xyz,mno)");
        assertEquals("abcmno", StringUtils.appendIfMissing("abcmno", "xyz", "mno"), "appendIfMissing(abcmno,xyz,mno)");
        assertEquals("abcXYZxyz", StringUtils.appendIfMissing("abcXYZ", "xyz", "mno"), "appendIfMissing(abcXYZ,xyz,mno)");
        assertEquals("abcMNOxyz", StringUtils.appendIfMissing("abcMNO", "xyz", "mno"), "appendIfMissing(abcMNO,xyz,mno)");
    }

    /**
     * Tests {@code appendIfMissingIgnoreCase}.
     */
    @Test
    void testAppendIfMissingIgnoreCase() {
        assertNull(StringUtils.appendIfMissingIgnoreCase(null, null), "appendIfMissingIgnoreCase(null,null)");
        assertEquals("abc", StringUtils.appendIfMissingIgnoreCase("abc", null), "appendIfMissingIgnoreCase(abc,null)");
        assertEquals("xyz", StringUtils.appendIfMissingIgnoreCase("", "xyz"), "appendIfMissingIgnoreCase(\"\",xyz)");
        assertEquals("abcxyz", StringUtils.appendIfMissingIgnoreCase("abc", "xyz"), "appendIfMissingIgnoreCase(abc,xyz)");
        assertEquals("abcxyz", StringUtils.appendIfMissingIgnoreCase("abcxyz", "xyz"), "appendIfMissingIgnoreCase(abcxyz,xyz)");
        assertEquals("abcXYZ", StringUtils.appendIfMissingIgnoreCase("abcXYZ", "xyz"), "appendIfMissingIgnoreCase(abcXYZ,xyz)");

        assertNull(StringUtils.appendIfMissingIgnoreCase(null, null, (CharSequence[]) null), "appendIfMissingIgnoreCase(null,null,null)");
        assertEquals("abc", StringUtils.appendIfMissingIgnoreCase("abc", null, (CharSequence[]) null), "appendIfMissingIgnoreCase(abc,null,null)");
        assertEquals("xyz", StringUtils.appendIfMissingIgnoreCase("", "xyz", (CharSequence[]) null), "appendIfMissingIgnoreCase(\"\",xyz,null)");
        assertEquals("abcxyz", StringUtils.appendIfMissingIgnoreCase("abc", "xyz", (CharSequence) null), "appendIfMissingIgnoreCase(abc,xyz,{null})");
        assertEquals("abc", StringUtils.appendIfMissingIgnoreCase("abc", "xyz", ""), "appendIfMissingIgnoreCase(abc,xyz,\"\")");
        assertEquals("abcxyz", StringUtils.appendIfMissingIgnoreCase("abc", "xyz", "mno"), "appendIfMissingIgnoreCase(abc,xyz,mno)");
        assertEquals("abcxyz", StringUtils.appendIfMissingIgnoreCase("abcxyz", "xyz", "mno"), "appendIfMissingIgnoreCase(abcxyz,xyz,mno)");
        assertEquals("abcmno", StringUtils.appendIfMissingIgnoreCase("abcmno", "xyz", "mno"), "appendIfMissingIgnoreCase(abcmno,xyz,mno)");
        assertEquals("abcXYZ", StringUtils.appendIfMissingIgnoreCase("abcXYZ", "xyz", "mno"), "appendIfMissingIgnoreCase(abcXYZ,xyz,mno)");
        assertEquals("abcMNO", StringUtils.appendIfMissingIgnoreCase("abcMNO", "xyz", "mno"), "appendIfMissingIgnoreCase(abcMNO,xyz,mno)");
    }

    @Test
    void testCapitalize() {
        assertNull(StringUtils.capitalize(null));

        assertEquals("", StringUtils.capitalize(""), "capitalize(empty-string) failed");
        assertEquals("X", StringUtils.capitalize("x"), "capitalize(single-char-string) failed");
        assertEquals(FOO_CAP, StringUtils.capitalize(FOO_CAP), "capitalize(String) failed");
        assertEquals(FOO_CAP, StringUtils.capitalize(FOO_UNCAP), "capitalize(string) failed");

        assertEquals("\u01C8", StringUtils.capitalize("\u01C9"), "capitalize(String) is not using TitleCase");

        // Javadoc examples
        assertNull(StringUtils.capitalize(null));
        assertEquals("", StringUtils.capitalize(""));
        assertEquals("Cat", StringUtils.capitalize("cat"));
        assertEquals("CAt", StringUtils.capitalize("cAt"));
        assertEquals("'cat'", StringUtils.capitalize("'cat'"));
    }

    @Test
    void testCenter_StringInt() {
        assertNull(StringUtils.center(null, -1));
        assertNull(StringUtils.center(null, 4));
        assertEquals("    ", StringUtils.center("", 4));
        assertEquals("ab", StringUtils.center("ab", 0));
        assertEquals("ab", StringUtils.center("ab", -1));
        assertEquals("ab", StringUtils.center("ab", 1));
        assertEquals("    ", StringUtils.center("", 4));
        assertEquals(" ab ", StringUtils.center("ab", 4));
        assertEquals("abcd", StringUtils.center("abcd", 2));
        assertEquals(" a  ", StringUtils.center("a", 4));
        assertEquals("  a  ", StringUtils.center("a", 5));
    }

    @Test
    void testCenter_StringIntChar() {
        assertNull(StringUtils.center(null, -1, ' '));
        assertNull(StringUtils.center(null, 4, ' '));
        assertEquals("    ", StringUtils.center("", 4, ' '));
        assertEquals("ab", StringUtils.center("ab", 0, ' '));
        assertEquals("ab", StringUtils.center("ab", -1, ' '));
        assertEquals("ab", StringUtils.center("ab", 1, ' '));
        assertEquals("    ", StringUtils.center("", 4, ' '));
        assertEquals(" ab ", StringUtils.center("ab", 4, ' '));
        assertEquals("abcd", StringUtils.center("abcd", 2, ' '));
        assertEquals(" a  ", StringUtils.center("a", 4, ' '));
        assertEquals("  a  ", StringUtils.center("a", 5, ' '));
        assertEquals("xxaxx", StringUtils.center("a", 5, 'x'));
    }

    @Test
    void testCenter_StringIntString() {
        assertNull(StringUtils.center(null, 4, null));
        assertNull(StringUtils.center(null, -1, " "));
        assertNull(StringUtils.center(null, 4, " "));
        assertEquals("    ", StringUtils.center("", 4, " "));
        assertEquals("ab", StringUtils.center("ab", 0, " "));
        assertEquals("ab", StringUtils.center("ab", -1, " "));
        assertEquals("ab", StringUtils.center("ab", 1, " "));
        assertEquals("    ", StringUtils.center("", 4, " "));
        assertEquals(" ab ", StringUtils.center("ab", 4, " "));
        assertEquals("abcd", StringUtils.center("abcd", 2, " "));
        assertEquals(" a  ", StringUtils.center("a", 4, " "));
        assertEquals("yayz", StringUtils.center("a", 4, "yz"));
        assertEquals("yzyayzy", StringUtils.center("a", 7, "yz"));
        assertEquals("  abc  ", StringUtils.center("abc", 7, null));
        assertEquals("  abc  ", StringUtils.center("abc", 7, ""));
    }

    @Test
    void testChomp() {

        final String[][] chompCases = {
                {FOO_UNCAP + "\r\n", FOO_UNCAP},
                {FOO_UNCAP + "\n", FOO_UNCAP},
                {FOO_UNCAP + "\r", FOO_UNCAP},
                {FOO_UNCAP + " \r", FOO_UNCAP + " "},
                {FOO_UNCAP, FOO_UNCAP},
                {FOO_UNCAP + "\n\n", FOO_UNCAP + "\n"},
                {FOO_UNCAP + "\r\n\r\n", FOO_UNCAP + "\r\n"},
                {"foo\nfoo", "foo\nfoo"},
                {"foo\n\rfoo", "foo\n\rfoo"},
                {"\n", ""},
                {"\r", ""},
                {"a", "a"},
                {"\r\n", ""},
                {"", ""},
                {null, null},
                {FOO_UNCAP + "\n\r", FOO_UNCAP + "\n"}
        };
        for (final String[] chompCase : chompCases) {
            final String original = chompCase[0];
            final String expectedResult = chompCase[1];
            assertEquals(expectedResult, StringUtils.chomp(original), "chomp(String) failed");
        }

        assertEquals("foo", StringUtils.chomp("foobar", "bar"), "chomp(String, String) failed");
        assertEquals("foobar", StringUtils.chomp("foobar", "baz"), "chomp(String, String) failed");
        assertEquals("foo", StringUtils.chomp("foo", "foooo"), "chomp(String, String) failed");
        assertEquals("foobar", StringUtils.chomp("foobar", ""), "chomp(String, String) failed");
        assertEquals("foobar", StringUtils.chomp("foobar", null), "chomp(String, String) failed");
        assertEquals("", StringUtils.chomp("", "foo"), "chomp(String, String) failed");
        assertEquals("", StringUtils.chomp("", null), "chomp(String, String) failed");
        assertEquals("", StringUtils.chomp("", ""), "chomp(String, String) failed");
        assertNull(StringUtils.chomp(null, "foo"), "chomp(String, String) failed");
        assertNull(StringUtils.chomp(null, null), "chomp(String, String) failed");
        assertNull(StringUtils.chomp(null, ""), "chomp(String, String) failed");
        assertEquals("", StringUtils.chomp("foo", "foo"), "chomp(String, String) failed");
        assertEquals(" ", StringUtils.chomp(" foo", "foo"), "chomp(String, String) failed");
        assertEquals("foo ", StringUtils.chomp("foo ", "foo"), "chomp(String, String) failed");
    }

    @Test
    void testChop() {

        final String[][] chopCases = {
                {FOO_UNCAP + "\r\n", FOO_UNCAP},
                {FOO_UNCAP + "\n", FOO_UNCAP},
                {FOO_UNCAP + "\r", FOO_UNCAP},
                {FOO_UNCAP + " \r", FOO_UNCAP + " "},
                {"foo", "fo"},
                {"foo\nfoo", "foo\nfo"},
                {"\n", ""},
                {"\r", ""},
                {"\r\n", ""},
                {null, null},
                {"", ""},
                {"a", ""},
        };
        for (final String[] chopCase : chopCases) {
            final String original = chopCase[0];
            final String expectedResult = chopCase[1];
            assertEquals(expectedResult, StringUtils.chop(original), "chop(String) failed");
        }
    }

    @Test
    void testConstructor() {
        assertNotNull(new StringUtils());
        final Constructor<?>[] cons = StringUtils.class.getDeclaredConstructors();
        assertEquals(1, cons.length);
        assertTrue(Modifier.isPublic(cons[0].getModifiers()));
        assertTrue(Modifier.isPublic(StringUtils.class.getModifiers()));
        assertFalse(Modifier.isFinal(StringUtils.class.getModifiers()));
    }

    @Test
    void testDefault_String() {
        assertEquals("", StringUtils.defaultString(null));
        assertEquals("", StringUtils.defaultString(""));
        assertEquals("abc", StringUtils.defaultString("abc"));
    }

    @Test
    void testDefault_StringString() {
        assertEquals("NULL", StringUtils.defaultString(null, "NULL"));
        assertEquals("", StringUtils.defaultString("", "NULL"));
        assertEquals("abc", StringUtils.defaultString("abc", "NULL"));
    }

    @Test
    void testDefaultIfBlank_CharBuffers() {
        assertEquals("NULL", StringUtils.defaultIfBlank(CharBuffer.wrap(""), CharBuffer.wrap("NULL")).toString());
        assertEquals("NULL", StringUtils.defaultIfBlank(CharBuffer.wrap(" "), CharBuffer.wrap("NULL")).toString());
        assertEquals("abc", StringUtils.defaultIfBlank(CharBuffer.wrap("abc"), CharBuffer.wrap("NULL")).toString());
        assertNull(StringUtils.defaultIfBlank(CharBuffer.wrap(""), (CharBuffer) null));
        // Tests compatibility for the API return type
        final CharBuffer s = StringUtils.defaultIfBlank(CharBuffer.wrap("abc"), CharBuffer.wrap("NULL"));
        assertEquals("abc", s.toString());
    }

    @Test
    void testDefaultIfBlank_StringBuffers() {
        assertEquals("NULL", StringUtils.defaultIfBlank(new StringBuffer(""), new StringBuffer("NULL")).toString());
        assertEquals("NULL", StringUtils.defaultIfBlank(new StringBuffer(" "), new StringBuffer("NULL")).toString());
        assertEquals("abc", StringUtils.defaultIfBlank(new StringBuffer("abc"), new StringBuffer("NULL")).toString());
        assertNull(StringUtils.defaultIfBlank(new StringBuffer(""), (StringBuffer) null));
        // Tests compatibility for the API return type
        final StringBuffer s = StringUtils.defaultIfBlank(new StringBuffer("abc"), new StringBuffer("NULL"));
        assertEquals("abc", s.toString());
    }

    @Test
    void testDefaultIfBlank_StringBuilders() {
        assertEquals("NULL", StringUtils.defaultIfBlank(new StringBuilder(""), new StringBuilder("NULL")).toString());
        assertEquals("NULL", StringUtils.defaultIfBlank(new StringBuilder(" "), new StringBuilder("NULL")).toString());
        assertEquals("abc", StringUtils.defaultIfBlank(new StringBuilder("abc"), new StringBuilder("NULL")).toString());
        assertNull(StringUtils.defaultIfBlank(new StringBuilder(""), (StringBuilder) null));
        // Tests compatibility for the API return type
        final StringBuilder s = StringUtils.defaultIfBlank(new StringBuilder("abc"), new StringBuilder("NULL"));
        assertEquals("abc", s.toString());
    }

    @Test
    void testDefaultIfBlank_StringString() {
        assertEquals("NULL", StringUtils.defaultIfBlank(null, "NULL"));
        assertEquals("NULL", StringUtils.defaultIfBlank("", "NULL"));
        assertEquals("NULL", StringUtils.defaultIfBlank(" ", "NULL"));
        assertEquals("abc", StringUtils.defaultIfBlank("abc", "NULL"));
        assertNull(StringUtils.defaultIfBlank("", (String) null));
        // Tests compatibility for the API return type
        final String s = StringUtils.defaultIfBlank("abc", "NULL");
        assertEquals("abc", s);
    }

    @Test
    void testDefaultIfEmpty_CharBuffers() {
        assertEquals("NULL", StringUtils.defaultIfEmpty(CharBuffer.wrap(""), CharBuffer.wrap("NULL")).toString());
        assertEquals("abc", StringUtils.defaultIfEmpty(CharBuffer.wrap("abc"), CharBuffer.wrap("NULL")).toString());
        assertNull(StringUtils.defaultIfEmpty(CharBuffer.wrap(""), (CharBuffer) null));
        // Tests compatibility for the API return type
        final CharBuffer s = StringUtils.defaultIfEmpty(CharBuffer.wrap("abc"), CharBuffer.wrap("NULL"));
        assertEquals("abc", s.toString());
    }

    @Test
    void testDefaultIfEmpty_StringBuffers() {
        assertEquals("NULL", StringUtils.defaultIfEmpty(new StringBuffer(""), new StringBuffer("NULL")).toString());
        assertEquals("abc", StringUtils.defaultIfEmpty(new StringBuffer("abc"), new StringBuffer("NULL")).toString());
        assertNull(StringUtils.defaultIfEmpty(new StringBuffer(""), (StringBuffer) null));
        // Tests compatibility for the API return type
        final StringBuffer s = StringUtils.defaultIfEmpty(new StringBuffer("abc"), new StringBuffer("NULL"));
        assertEquals("abc", s.toString());
    }

    @Test
    void testDefaultIfEmpty_StringBuilders() {
        assertEquals("NULL", StringUtils.defaultIfEmpty(new StringBuilder(""), new StringBuilder("NULL")).toString());
        assertEquals("abc", StringUtils.defaultIfEmpty(new StringBuilder("abc"), new StringBuilder("NULL")).toString());
        assertNull(StringUtils.defaultIfEmpty(new StringBuilder(""), (StringBuilder) null));
        // Tests compatibility for the API return type
        final StringBuilder s = StringUtils.defaultIfEmpty(new StringBuilder("abc"), new StringBuilder("NULL"));
        assertEquals("abc", s.toString());
    }

    @Test
    void testDefaultIfEmpty_StringString() {
        assertEquals("NULL", StringUtils.defaultIfEmpty(null, "NULL"));
        assertEquals("NULL", StringUtils.defaultIfEmpty("", "NULL"));
        assertEquals("abc", StringUtils.defaultIfEmpty("abc", "NULL"));
        assertNull(StringUtils.getIfEmpty("", null));
        // Tests compatibility for the API return type
        final String s = StringUtils.defaultIfEmpty("abc", "NULL");
        assertEquals("abc", s);
    }

    @Test
    void testDeleteWhitespace_String() {
        assertNull(StringUtils.deleteWhitespace(null));
        assertEquals("", StringUtils.deleteWhitespace(""));
        assertEquals("", StringUtils.deleteWhitespace("  \u000C  \t\t\u001F\n\n \u000B  "));
        assertEquals("", StringUtils.deleteWhitespace(StringUtilsTest.WHITESPACE));
        assertEquals(StringUtilsTest.NON_WHITESPACE, StringUtils.deleteWhitespace(StringUtilsTest.NON_WHITESPACE));
        // Note: u-2007 and u-000A both cause problems in the source code
        // it should ignore 2007 but delete 000A
        assertEquals("\u00A0\u202F", StringUtils.deleteWhitespace("  \u00A0  \t\t\n\n \u202F  "));
        assertEquals("\u00A0\u202F", StringUtils.deleteWhitespace("\u00A0\u202F"));
        assertEquals("test", StringUtils.deleteWhitespace("\u000Bt  \t\n\u0009e\rs\n\n   \tt"));
    }

    @Test
    void testDifference_StringString() {
        assertNull(StringUtils.difference(null, null));
        assertEquals("", StringUtils.difference("", ""));
        assertEquals("abc", StringUtils.difference("", "abc"));
        assertEquals("", StringUtils.difference("abc", ""));
        assertEquals("i am a robot", StringUtils.difference(null, "i am a robot"));
        assertEquals("i am a machine", StringUtils.difference("i am a machine", null));
        assertEquals("robot", StringUtils.difference("i am a machine", "i am a robot"));
        assertEquals("", StringUtils.difference("abc", "abc"));
        assertEquals("you are a robot", StringUtils.difference("i am a robot", "you are a robot"));
        // 0x10400 and 0x10401 share the same high surrogate; the difference must not begin with a lone low surrogate
        final String cp10400 = new String(Character.toChars(0x10400));
        final String cp10401 = new String(Character.toChars(0x10401));
        assertEquals(cp10401, StringUtils.difference(cp10400, cp10401));
        assertEquals("Y", StringUtils.difference(cp10400 + "X", cp10400 + "Y"));
    }

    @Test
    void testDifferenceAt_StringArray() {
        assertEquals(-1, StringUtils.indexOfDifference((String[]) null));
        assertEquals(-1, StringUtils.indexOfDifference());
        assertEquals(-1, StringUtils.indexOfDifference("abc"));
        assertEquals(-1, StringUtils.indexOfDifference(null, null));
        assertEquals(-1, StringUtils.indexOfDifference("", ""));
        assertEquals(0, StringUtils.indexOfDifference("", null));
        assertEquals(0, StringUtils.indexOfDifference("abc", null, null));
        assertEquals(0, StringUtils.indexOfDifference(null, null, "abc"));
        assertEquals(0, StringUtils.indexOfDifference("", "abc"));
        assertEquals(0, StringUtils.indexOfDifference("abc", ""));
        assertEquals(-1, StringUtils.indexOfDifference("abc", "abc"));
        assertEquals(1, StringUtils.indexOfDifference("abc", "a"));
        assertEquals(2, StringUtils.indexOfDifference("ab", "abxyz"));
        assertEquals(2, StringUtils.indexOfDifference("abcde", "abxyz"));
        assertEquals(0, StringUtils.indexOfDifference("abcde", "xyz"));
        assertEquals(0, StringUtils.indexOfDifference("xyz", "abcde"));
        assertEquals(7, StringUtils.indexOfDifference("i am a machine", "i am a robot"));
        // a difference that falls inside a shared surrogate pair is reported at the start of the pair, not mid-pair
        final String cp10400 = new String(Character.toChars(0x10400));
        final String cp10401 = new String(Character.toChars(0x10401));
        assertEquals(0, StringUtils.indexOfDifference(new String[] {cp10400, cp10401}));
        assertEquals(2, StringUtils.indexOfDifference(new String[] {cp10400 + "X", cp10400 + "Y"}));
    }

    @Test
    void testDifferenceAt_StringString() {
        assertEquals(-1, StringUtils.indexOfDifference(null, null));
        assertEquals(0, StringUtils.indexOfDifference(null, "i am a robot"));
        assertEquals(-1, StringUtils.indexOfDifference("", ""));
        assertEquals(0, StringUtils.indexOfDifference("", "abc"));
        assertEquals(0, StringUtils.indexOfDifference("abc", ""));
        assertEquals(0, StringUtils.indexOfDifference("i am a machine", null));
        assertEquals(7, StringUtils.indexOfDifference("i am a machine", "i am a robot"));
        assertEquals(-1, StringUtils.indexOfDifference("foo", "foo"));
        assertEquals(0, StringUtils.indexOfDifference("i am a robot", "you are a robot"));
        // a difference that falls inside a shared surrogate pair is reported at the start of the pair, not mid-pair
        final String cp10400 = new String(Character.toChars(0x10400));
        final String cp10401 = new String(Character.toChars(0x10401));
        assertEquals(0, StringUtils.indexOfDifference(cp10400, cp10401));
        assertEquals(2, StringUtils.indexOfDifference(cp10400 + "X", cp10400 + "Y"));
    }

    /**
     * A sanity check for {@link StringUtils#EMPTY}.
     */
    @Test
    void testEMPTY() {
        assertNotNull(StringUtils.EMPTY);
        assertEquals("", StringUtils.EMPTY);
        assertEquals(0, StringUtils.EMPTY.length());
    }

    @Test
    void testEscapeSurrogatePairs() {
        assertEquals("\uD83D\uDE30", StringEscapeUtils.escapeCsv("\uD83D\uDE30"));
        // Examples from https://en.wikipedia.org/wiki/UTF-16
        assertEquals("\uD800\uDC00", StringEscapeUtils.escapeCsv("\uD800\uDC00"));
        assertEquals("\uD834\uDD1E", StringEscapeUtils.escapeCsv("\uD834\uDD1E"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.escapeCsv("\uDBFF\uDFFD"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.escapeHtml3("\uDBFF\uDFFD"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.escapeHtml4("\uDBFF\uDFFD"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.escapeXml("\uDBFF\uDFFD"));
    }

    /**
     * Tests LANG-858.
     */
    @Test
    void testEscapeSurrogatePairsLang858() {
        assertEquals("\\uDBFF\\uDFFD", StringEscapeUtils.escapeJava("\uDBFF\uDFFD"));       //fail LANG-858
        assertEquals("\\uDBFF\\uDFFD", StringEscapeUtils.escapeEcmaScript("\uDBFF\uDFFD")); //fail LANG-858
    }

    @Test
    void testGeorgianSample() {
        final char[] arrayI = {
                //Latin Small Letter dotless I
                (char) 0x0131,
                //Greek Capital Letter Theta
                (char) 0x03F4
        };
        final char[] arrayJ = {
                //Latin Capital Letter I with dot above
                (char) 0x0130,
                //Greek Theta Symbol
                (char) 0x03D1
        };
        for (final char i : arrayI) {
            for (final char j : arrayJ) {
                final String si = String.valueOf(i);
                final String sj = String.valueOf(j);
                final boolean res1 = si.equalsIgnoreCase(sj);
                final CharSequence ci = new StringBuilder(si);
                final CharSequence cj = new StringBuilder(sj);
                boolean res2 = StringUtils.startsWithIgnoreCase(ci, cj);
                assertEquals(res1, res2, "si : " + si + " sj : " + sj);
                res2 = StringUtils.endsWithIgnoreCase(ci, cj);
                assertEquals(res1, res2, "si : " + si + " sj : " + sj);
                res2 = StringUtils.compareIgnoreCase(ci.toString(), cj.toString()) == 0;
                assertEquals(res1, res2, "si : " + si + " sj : " + sj);
                res2 = StringUtils.indexOfIgnoreCase(ci.toString(), cj.toString()) == 0;
                assertEquals(res1, res2, "si : " + si + " sj : " + sj);
                res2 = StringUtils.lastIndexOfIgnoreCase(ci.toString(), cj.toString()) == 0;
                assertEquals(res1, res2, "si : " + si + " sj : " + sj);
            }
        }
    }

    @Test
    void testGetBytes_Charset() {
        assertEquals(ArrayUtils.EMPTY_BYTE_ARRAY, StringUtils.getBytes(null, (Charset) null));
        assertArrayEquals(StringUtils.EMPTY.getBytes(), StringUtils.getBytes(StringUtils.EMPTY, (Charset) null));
        assertArrayEquals(StringUtils.EMPTY.getBytes(StandardCharsets.US_ASCII),
            StringUtils.getBytes(StringUtils.EMPTY, StandardCharsets.US_ASCII));
    }

    @Test
    void testGetBytes_String() throws UnsupportedEncodingException {
        assertEquals(ArrayUtils.EMPTY_BYTE_ARRAY, StringUtils.getBytes(null, (String) null));
        assertArrayEquals(StringUtils.EMPTY.getBytes(), StringUtils.getBytes(StringUtils.EMPTY, (String) null));
        assertArrayEquals(StringUtils.EMPTY.getBytes(StandardCharsets.US_ASCII.name()),
            StringUtils.getBytes(StringUtils.EMPTY, StandardCharsets.US_ASCII.name()));
    }

    @Test
    void testGetCommonPrefix_StringArray() {
        assertEquals("", StringUtils.getCommonPrefix((String[]) null));
        assertEquals("", StringUtils.getCommonPrefix());
        assertEquals("abc", StringUtils.getCommonPrefix("abc"));
        assertEquals("", StringUtils.getCommonPrefix(null, null));
        assertEquals("", StringUtils.getCommonPrefix("", ""));
        assertEquals("", StringUtils.getCommonPrefix("", null));
        assertEquals("", StringUtils.getCommonPrefix("abc", null, null));
        assertEquals("", StringUtils.getCommonPrefix(null, null, "abc"));
        assertEquals("", StringUtils.getCommonPrefix("", "abc"));
        assertEquals("", StringUtils.getCommonPrefix("abc", ""));
        assertEquals("abc", StringUtils.getCommonPrefix("abc", "abc"));
        assertEquals("a", StringUtils.getCommonPrefix("abc", "a"));
        assertEquals("ab", StringUtils.getCommonPrefix("ab", "abxyz"));
        assertEquals("ab", StringUtils.getCommonPrefix("abcde", "abxyz"));
        assertEquals("", StringUtils.getCommonPrefix("abcde", "xyz"));
        assertEquals("", StringUtils.getCommonPrefix("xyz", "abcde"));
        assertEquals("i am a ", StringUtils.getCommonPrefix("i am a machine", "i am a robot"));
        // 0x10400 and 0x10401 share the high surrogate but differ; the common prefix must not be a lone high surrogate
        final String cp10400 = new String(Character.toChars(0x10400));
        final String cp10401 = new String(Character.toChars(0x10401));
        assertEquals("", StringUtils.getCommonPrefix(cp10400, cp10401));
        assertEquals(cp10400, StringUtils.getCommonPrefix(cp10400 + "X", cp10400 + "Y"));
    }

    @Test
    void testGetDigits() {
        assertNull(StringUtils.getDigits(null));
        assertEquals("", StringUtils.getDigits(""));
        assertEquals("", StringUtils.getDigits("abc"));
        assertEquals("1000", StringUtils.getDigits("1000$"));
        assertEquals("12345", StringUtils.getDigits("123password45"));
        assertEquals("5417543010", StringUtils.getDigits("(541) 754-3010"));
        assertEquals("\u0967\u0968\u0969", StringUtils.getDigits("\u0967\u0968\u0969"));
    }

    @Test
    void testGetDigitsKeycaps() {
        assertEquals("0123456789", StringUtils.getDigits("0️⃣1️⃣2️⃣3️⃣4️⃣5️⃣6️⃣7️⃣8️⃣9️⃣#️⃣"));
    }

    @Test
    void testGetDigitsSupplementary() {
        // U+1D7CF MATHEMATICAL BOLD DIGIT ONE: Character.isDigit is true but it is a surrogate pair
        final String mathOne = new String(Character.toChars(0x1D7CF));
        assertEquals(mathOne, StringUtils.getDigits(mathOne));
        assertEquals(mathOne + "9", StringUtils.getDigits("a" + mathOne + "9"));
    }

    @Test
    void testGetFuzzyDistance() {
        assertEquals(0, StringUtils.getFuzzyDistance("", "", Locale.ENGLISH));
        assertEquals(0, StringUtils.getFuzzyDistance("Workshop", "b", Locale.ENGLISH));
        assertEquals(1, StringUtils.getFuzzyDistance("Room", "o", Locale.ENGLISH));
        assertEquals(1, StringUtils.getFuzzyDistance("Workshop", "w", Locale.ENGLISH));
        assertEquals(2, StringUtils.getFuzzyDistance("Workshop", "ws", Locale.ENGLISH));
        assertEquals(4, StringUtils.getFuzzyDistance("Workshop", "wo", Locale.ENGLISH));
        assertEquals(3, StringUtils.getFuzzyDistance("Apache Software Foundation", "asf", Locale.ENGLISH));
    }

    @Test
    void testGetFuzzyDistance_NullNullNull() {
        assertIllegalArgumentException(() -> StringUtils.getFuzzyDistance(null, null, null));
    }

    @Test
    void testGetFuzzyDistance_NullStringLocale() {
        assertIllegalArgumentException(() -> StringUtils.getFuzzyDistance(null, "clear", Locale.ENGLISH));
    }

    @Test
    void testGetFuzzyDistance_StringNullLoclae() {
        assertIllegalArgumentException(() -> StringUtils.getFuzzyDistance(" ", null, Locale.ENGLISH));
    }

    @Test
    void testGetFuzzyDistance_StringStringNull() {
        assertIllegalArgumentException(() -> StringUtils.getFuzzyDistance(" ", "clear", null));
    }

    @Test
    void testGetIfBlank_StringStringSupplier() {
        assertEquals("NULL", StringUtils.getIfBlank(null, () -> "NULL"));
        assertEquals("NULL", StringUtils.getIfBlank("",  () -> "NULL"));
        assertEquals("NULL", StringUtils.getIfBlank(" ", () -> "NULL"));
        assertEquals("abc", StringUtils.getIfBlank("abc", () -> "NULL"));
        assertNull(StringUtils.getIfBlank("", Suppliers.nul()));
        assertNull(StringUtils.defaultIfBlank("", (String) null));
        // Tests compatibility for the API return type
        final String s = StringUtils.getIfBlank("abc", () -> "NULL");
        assertEquals("abc", s);
        //Checking that default value supplied only on demand
        final MutableInt numberOfCalls = new MutableInt(0);
        final Supplier<String> countingDefaultSupplier = () -> {
            numberOfCalls.increment();
            return "NULL";
        };
        StringUtils.getIfBlank("abc", countingDefaultSupplier);
        assertEquals(0, numberOfCalls.get());
        StringUtils.getIfBlank("", countingDefaultSupplier);
        assertEquals(1, numberOfCalls.get());
        StringUtils.getIfBlank(" ", countingDefaultSupplier);
        assertEquals(2, numberOfCalls.get());
        StringUtils.getIfBlank(null, countingDefaultSupplier);
        assertEquals(3, numberOfCalls.get());
    }

    @Test
    void testGetIfEmpty_StringStringSupplier() {
        assertEquals("NULL", StringUtils.getIfEmpty((String) null, () -> "NULL"));
        assertEquals("NULL", StringUtils.getIfEmpty("", () -> "NULL"));
        assertEquals("abc", StringUtils.getIfEmpty("abc", () -> "NULL"));
        assertNull(StringUtils.getIfEmpty("", Suppliers.nul()));
        assertNull(StringUtils.defaultIfEmpty("", (String) null));
        // Tests compatibility for the API return type
        final String s = StringUtils.getIfEmpty("abc", () -> "NULL");
        assertEquals("abc", s);
        //Checking that default value supplied only on demand
        final MutableInt numberOfCalls = new MutableInt(0);
        final Supplier<String> countingDefaultSupplier = () -> {
            numberOfCalls.increment();
            return "NULL";
        };
        StringUtils.getIfEmpty("abc", countingDefaultSupplier);
        assertEquals(0, numberOfCalls.get());
        StringUtils.getIfEmpty("", countingDefaultSupplier);
        assertEquals(1, numberOfCalls.get());
        StringUtils.getIfEmpty(null, countingDefaultSupplier);
        assertEquals(2, numberOfCalls.get());
    }

    @Test
    void testGetJaroWinklerDistance_NullNull() {
        assertIllegalArgumentException(() -> StringUtils.getJaroWinklerDistance(null, null));
    }

    @Test
    void testGetJaroWinklerDistance_NullString() {
        assertIllegalArgumentException(() -> StringUtils.getJaroWinklerDistance(null, "clear"));
    }

    @Test
    void testGetJaroWinklerDistance_StringNull() {
        assertIllegalArgumentException(() -> StringUtils.getJaroWinklerDistance(" ", null));
    }

    @Test
    void testGetJaroWinklerDistance_StringString() {
        assertEquals(0.93d, StringUtils.getJaroWinklerDistance("frog", "fog"));
        assertEquals(0.0d, StringUtils.getJaroWinklerDistance("fly", "ant"));
        assertEquals(0.44d, StringUtils.getJaroWinklerDistance("elephant", "hippo"));
        assertEquals(0.84d, StringUtils.getJaroWinklerDistance("dwayne", "duane"));
        assertEquals(0.93d, StringUtils.getJaroWinklerDistance("ABC Corporation", "ABC Corp"));
        assertEquals(0.95d, StringUtils.getJaroWinklerDistance("D N H Enterprises Inc", "D & H Enterprises, Inc."));
        assertEquals(0.92d, StringUtils.getJaroWinklerDistance("My Gym Children's Fitness Center", "My Gym. Childrens Fitness"));
        assertEquals(0.88d, StringUtils.getJaroWinklerDistance("PENNSYLVANIA", "PENNCISYLVNIA"));
        assertEquals(0.63d, StringUtils.getJaroWinklerDistance("Haus Ingeborg", "Ingeborg Esser"));
    }

    @Test
    void testGetLevenshteinDistance_NullString() {
        assertIllegalArgumentException(() -> StringUtils.getLevenshteinDistance("a", null));
    }

    @Test
    void testGetLevenshteinDistance_NullStringInt() {
        assertIllegalArgumentException(() -> StringUtils.getLevenshteinDistance(null, "a", 0));
    }

    @Test
    void testGetLevenshteinDistance_StringNull() {
        assertIllegalArgumentException(() -> StringUtils.getLevenshteinDistance(null, "a"));
    }

    @Test
    void testGetLevenshteinDistance_StringNullInt() {
        assertIllegalArgumentException(() -> StringUtils.getLevenshteinDistance("a", null, 0));
    }

    @Test
    void testGetLevenshteinDistance_StringString() {
        assertEquals(0, StringUtils.getLevenshteinDistance("", ""));
        assertEquals(1, StringUtils.getLevenshteinDistance("", "a"));
        assertEquals(7, StringUtils.getLevenshteinDistance("aaapppp", ""));
        assertEquals(1, StringUtils.getLevenshteinDistance("frog", "fog"));
        assertEquals(3, StringUtils.getLevenshteinDistance("fly", "ant"));
        assertEquals(7, StringUtils.getLevenshteinDistance("elephant", "hippo"));
        assertEquals(7, StringUtils.getLevenshteinDistance("hippo", "elephant"));
        assertEquals(8, StringUtils.getLevenshteinDistance("hippo", "zzzzzzzz"));
        assertEquals(8, StringUtils.getLevenshteinDistance("zzzzzzzz", "hippo"));
        assertEquals(1, StringUtils.getLevenshteinDistance("hello", "hallo"));
    }

    @Test
    void testGetLevenshteinDistance_StringStringInt() {
        // empty strings
        assertEquals(0, StringUtils.getLevenshteinDistance("", "", 0));
        assertEquals(7, StringUtils.getLevenshteinDistance("aaapppp", "", 8));
        assertEquals(7, StringUtils.getLevenshteinDistance("aaapppp", "", 7));
        assertEquals(-1, StringUtils.getLevenshteinDistance("aaapppp", "", 6));

        // unequal strings, zero threshold
        assertEquals(-1, StringUtils.getLevenshteinDistance("b", "a", 0));
        assertEquals(-1, StringUtils.getLevenshteinDistance("a", "b", 0));

        // equal strings
        assertEquals(0, StringUtils.getLevenshteinDistance("aa", "aa", 0));
        assertEquals(0, StringUtils.getLevenshteinDistance("aa", "aa", 2));

        // same length
        assertEquals(-1, StringUtils.getLevenshteinDistance("aaa", "bbb", 2));
        assertEquals(3, StringUtils.getLevenshteinDistance("aaa", "bbb", 3));

        // big stripe
        assertEquals(6, StringUtils.getLevenshteinDistance("aaaaaa", "b", 10));

        // distance less than threshold
        assertEquals(7, StringUtils.getLevenshteinDistance("aaapppp", "b", 8));
        assertEquals(3, StringUtils.getLevenshteinDistance("a", "bbb", 4));

        // distance equal to threshold
        assertEquals(7, StringUtils.getLevenshteinDistance("aaapppp", "b", 7));
        assertEquals(3, StringUtils.getLevenshteinDistance("a", "bbb", 3));

        // distance greater than threshold
        assertEquals(-1, StringUtils.getLevenshteinDistance("a", "bbb", 2));
        assertEquals(-1, StringUtils.getLevenshteinDistance("bbb", "a", 2));
        assertEquals(-1, StringUtils.getLevenshteinDistance("aaapppp", "b", 6));

        // stripe runs off array, strings not similar
        assertEquals(-1, StringUtils.getLevenshteinDistance("a", "bbb", 1));
        assertEquals(-1, StringUtils.getLevenshteinDistance("bbb", "a", 1));

        // stripe runs off array, strings are similar
        assertEquals(-1, StringUtils.getLevenshteinDistance("12345", "1234567", 1));
        assertEquals(-1, StringUtils.getLevenshteinDistance("1234567", "12345", 1));

        // old getLevenshteinDistance test cases
        assertEquals(1, StringUtils.getLevenshteinDistance("frog", "fog", 1));
        assertEquals(3, StringUtils.getLevenshteinDistance("fly", "ant", 3));
        assertEquals(7, StringUtils.getLevenshteinDistance("elephant", "hippo", 7));
        assertEquals(-1, StringUtils.getLevenshteinDistance("elephant", "hippo", 6));
        assertEquals(7, StringUtils.getLevenshteinDistance("hippo", "elephant", 7));
        assertEquals(-1, StringUtils.getLevenshteinDistance("hippo", "elephant", 6));
        assertEquals(8, StringUtils.getLevenshteinDistance("hippo", "zzzzzzzz", 8));
        assertEquals(8, StringUtils.getLevenshteinDistance("zzzzzzzz", "hippo", 8));
        assertEquals(1, StringUtils.getLevenshteinDistance("hello", "hallo", 1));

        assertEquals(1, StringUtils.getLevenshteinDistance("frog", "fog", Integer.MAX_VALUE));
        assertEquals(3, StringUtils.getLevenshteinDistance("fly", "ant", Integer.MAX_VALUE));
        assertEquals(7, StringUtils.getLevenshteinDistance("elephant", "hippo", Integer.MAX_VALUE));
        assertEquals(7, StringUtils.getLevenshteinDistance("hippo", "elephant", Integer.MAX_VALUE));
        assertEquals(8, StringUtils.getLevenshteinDistance("hippo", "zzzzzzzz", Integer.MAX_VALUE));
        assertEquals(8, StringUtils.getLevenshteinDistance("zzzzzzzz", "hippo", Integer.MAX_VALUE));
        assertEquals(1, StringUtils.getLevenshteinDistance("hello", "hallo", Integer.MAX_VALUE));
    }

    @Test
    void testGetLevenshteinDistance_StringStringNegativeInt() {
        assertIllegalArgumentException(() -> StringUtils.getLevenshteinDistance("a", "a", -1));
    }

    /**
     * Test for {@link StringUtils#isAllLowerCase(CharSequence)}.
     */
    @Test
    void testIsAllLowerCase() {
        assertFalse(StringUtils.isAllLowerCase(null));
        assertFalse(StringUtils.isAllLowerCase(StringUtils.EMPTY));
        assertFalse(StringUtils.isAllLowerCase("  "));
        assertTrue(StringUtils.isAllLowerCase("abc"));
        assertFalse(StringUtils.isAllLowerCase("abc "));
        assertFalse(StringUtils.isAllLowerCase("abc\n"));
        assertFalse(StringUtils.isAllLowerCase("abC"));
        assertFalse(StringUtils.isAllLowerCase("ab c"));
        assertFalse(StringUtils.isAllLowerCase("ab1c"));
        assertFalse(StringUtils.isAllLowerCase("ab/c"));
    }

    /**
     * Test for {@link StringUtils#isAllLowerCase(CharSequence)} with supplementary code points.
     */
    @Test
    void testIsAllLowerCaseSupplementary() {
        // U+10428 DESERET SMALL LETTER LONG I is a lowercase supplementary letter
        assertTrue(StringUtils.isAllLowerCase(new String(Character.toChars(0x10428))));
        // U+10400 DESERET CAPITAL LETTER LONG I is an uppercase supplementary letter
        assertFalse(StringUtils.isAllLowerCase(new String(Character.toChars(0x10400))));
    }

    /**
     * Test for {@link StringUtils#isAllUpperCase(CharSequence)}.
     */
    @Test
    void testIsAllUpperCase() {
        assertFalse(StringUtils.isAllUpperCase(null));
        assertFalse(StringUtils.isAllUpperCase(StringUtils.EMPTY));
        assertFalse(StringUtils.isAllUpperCase("  "));
        assertTrue(StringUtils.isAllUpperCase("ABC"));
        assertFalse(StringUtils.isAllUpperCase("ABC "));
        assertFalse(StringUtils.isAllUpperCase("ABC\n"));
        assertFalse(StringUtils.isAllUpperCase("aBC"));
        assertFalse(StringUtils.isAllUpperCase("A C"));
        assertFalse(StringUtils.isAllUpperCase("A1C"));
        assertFalse(StringUtils.isAllUpperCase("A/C"));
    }

    /**
     * Test for {@link StringUtils#isAllUpperCase(CharSequence)} with supplementary code points.
     */
    @Test
    void testIsAllUpperCaseSupplementary() {
        // U+10400 DESERET CAPITAL LETTER LONG I is an uppercase supplementary letter
        assertTrue(StringUtils.isAllUpperCase(new String(Character.toChars(0x10400))));
        // U+10428 DESERET SMALL LETTER LONG I is a lowercase supplementary letter
        assertFalse(StringUtils.isAllUpperCase(new String(Character.toChars(0x10428))));
    }

    /**
     * Test for {@link StringUtils#isMixedCase(CharSequence)}.
     */
    @Test
    void testIsMixedCase() {
        assertFalse(StringUtils.isMixedCase(null));
        assertFalse(StringUtils.isMixedCase(StringUtils.EMPTY));
        assertFalse(StringUtils.isMixedCase(" "));
        assertFalse(StringUtils.isMixedCase("A"));
        assertFalse(StringUtils.isMixedCase("a"));
        assertFalse(StringUtils.isMixedCase("/"));
        assertFalse(StringUtils.isMixedCase("A/"));
        assertFalse(StringUtils.isMixedCase("/b"));
        assertFalse(StringUtils.isMixedCase("abc"));
        assertFalse(StringUtils.isMixedCase("ABC"));
        assertTrue(StringUtils.isMixedCase("aBc"));
        assertTrue(StringUtils.isMixedCase("aBc "));
        assertTrue(StringUtils.isMixedCase("A c"));
        assertTrue(StringUtils.isMixedCase("aBc\n"));
        assertTrue(StringUtils.isMixedCase("A1c"));
        assertTrue(StringUtils.isMixedCase("a/C"));
    }

    /**
     * Test for {@link StringUtils#isMixedCase(CharSequence)} with supplementary code points.
     */
    @Test
    void testIsMixedCaseSupplementary() {
        // lowercase 'a' mixed with the uppercase supplementary letter U+10400
        assertTrue(StringUtils.isMixedCase("a" + new String(Character.toChars(0x10400))));
        // a single uppercase supplementary letter is not mixed case
        assertFalse(StringUtils.isMixedCase(new String(Character.toChars(0x10400))));
    }

    @Test
    void testJoin_ArrayCharSeparator() {
        assertNull(StringUtils.join((Object[]) null, ','));
        assertEquals(TEXT_LIST_CHAR, StringUtils.join(ARRAY_LIST, SEPARATOR_CHAR));
        assertEquals("", StringUtils.join(EMPTY_ARRAY_LIST, SEPARATOR_CHAR));
        assertEquals(";;foo", StringUtils.join(MIXED_ARRAY_LIST, SEPARATOR_CHAR));
        assertEquals("foo;2", StringUtils.join(MIXED_TYPE_LIST, SEPARATOR_CHAR));

        assertNull(StringUtils.join((Object[]) null, ',', 0, 1));
        assertEquals("/", StringUtils.join(MIXED_ARRAY_LIST, '/', 0, MIXED_ARRAY_LIST.length - 1));
        assertEquals("foo", StringUtils.join(MIXED_TYPE_LIST, '/', 0, 1));
        assertEquals("null", StringUtils.join(NULL_TO_STRING_LIST, '/', 0, 1));
        assertEquals("foo/2", StringUtils.join(MIXED_TYPE_LIST, '/', 0, 2));
        assertEquals("2", StringUtils.join(MIXED_TYPE_LIST, '/', 1, 2));
        assertEquals("", StringUtils.join(MIXED_TYPE_LIST, '/', 2, 1));
    }

    @Test
    void testJoin_ArrayOfBooleans() {
        assertNull(StringUtils.join((boolean[]) null, COMMA_SEPARATOR_CHAR));
        assertEquals("false;false", StringUtils.join(ARRAY_FALSE_FALSE, SEPARATOR_CHAR));
        assertEquals("", StringUtils.join(EMPTY, SEPARATOR_CHAR));
        assertEquals("false,true,false", StringUtils.join(ARRAY_FALSE_TRUE_FALSE, COMMA_SEPARATOR_CHAR));
        assertEquals("true", StringUtils.join(ARRAY_FALSE_TRUE, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((boolean[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(ARRAY_FALSE_FALSE, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(ARRAY_FALSE_TRUE_FALSE, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfBytes() {
        assertNull(StringUtils.join((byte[]) null, ','));
        assertEquals("1;2", StringUtils.join(BYTE_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2", StringUtils.join(BYTE_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((byte[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(BYTE_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(BYTE_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfChars() {
        assertNull(StringUtils.join((char[]) null, ','));
        assertEquals("1;2", StringUtils.join(CHAR_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2", StringUtils.join(CHAR_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((char[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(CHAR_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(CHAR_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfDoubles() {
        assertNull(StringUtils.join((double[]) null, ','));
        assertEquals("1.0;2.0", StringUtils.join(DOUBLE_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2.0", StringUtils.join(DOUBLE_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((double[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(DOUBLE_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(DOUBLE_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfFloats() {
        assertNull(StringUtils.join((float[]) null, ','));
        assertEquals("1.0;2.0", StringUtils.join(FLOAT_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2.0", StringUtils.join(FLOAT_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((float[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(FLOAT_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(FLOAT_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfInts() {
        assertNull(StringUtils.join((int[]) null, ','));
        assertEquals("1;2", StringUtils.join(INT_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2", StringUtils.join(INT_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((int[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(INT_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(INT_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfLongs() {
        assertNull(StringUtils.join((long[]) null, ','));
        assertEquals("1;2", StringUtils.join(LONG_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2", StringUtils.join(LONG_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((long[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(LONG_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(LONG_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayOfShorts() {
        assertNull(StringUtils.join((short[]) null, ','));
        assertEquals("1;2", StringUtils.join(SHORT_PRIM_LIST, SEPARATOR_CHAR));
        assertEquals("2", StringUtils.join(SHORT_PRIM_LIST, SEPARATOR_CHAR, 1, 2));
        assertNull(StringUtils.join((short[]) null, SEPARATOR_CHAR, 0, 1));
        assertEquals(StringUtils.EMPTY, StringUtils.join(SHORT_PRIM_LIST, SEPARATOR_CHAR, 0, 0));
        assertEquals(StringUtils.EMPTY, StringUtils.join(SHORT_PRIM_LIST, SEPARATOR_CHAR, 1, 0));
    }

    @Test
    void testJoin_ArrayString_EmptyDelimiter() {
        assertNull(StringUtils.join((Object[]) null, null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(ARRAY_LIST, null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(ARRAY_LIST, ""));

        assertEquals("", StringUtils.join(NULL_ARRAY_LIST, null));

        assertEquals("", StringUtils.join(EMPTY_ARRAY_LIST, null));
        assertEquals("", StringUtils.join(EMPTY_ARRAY_LIST, ""));

        assertEquals("", StringUtils.join(MIXED_ARRAY_LIST, "", 0, MIXED_ARRAY_LIST.length - 1));
    }

    @ParameterizedTest
    @ValueSource(strings = {",", ";", Supplementary.CharU20000, Supplementary.CharU20001})
    void testJoin_ArrayString_NonEmptyDelimiter(final String delimiter) {
        assertEquals("", StringUtils.join(EMPTY_ARRAY_LIST, delimiter));

        assertEquals(String.join(delimiter, ARRAY_LIST), StringUtils.join(ARRAY_LIST, delimiter));
        assertEquals(delimiter + delimiter + "foo", StringUtils.join(MIXED_ARRAY_LIST, delimiter));
        assertEquals(String.join(delimiter, "foo", "2"), StringUtils.join(MIXED_TYPE_LIST, delimiter));

        assertEquals(delimiter, StringUtils.join(MIXED_ARRAY_LIST, delimiter, 0, MIXED_ARRAY_LIST.length - 1));
        assertEquals("foo", StringUtils.join(MIXED_TYPE_LIST, delimiter, 0, 1));
        assertEquals(String.join(delimiter, "foo", "2"), StringUtils.join(MIXED_TYPE_LIST, delimiter, 0, 2));
        assertEquals("2", StringUtils.join(MIXED_TYPE_LIST, delimiter, 1, 2));
        assertEquals("", StringUtils.join(MIXED_TYPE_LIST, delimiter, 2, 1));
    }

    @Test
    void testJoin_IterableChar() {
        assertNull(StringUtils.join((Iterable<?>) null, ','));
        assertEquals(TEXT_LIST_CHAR, StringUtils.join(Arrays.asList(ARRAY_LIST), SEPARATOR_CHAR));
        assertEquals("", StringUtils.join(Arrays.asList(NULL_ARRAY_LIST), SEPARATOR_CHAR));
        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST), SEPARATOR_CHAR));
        assertEquals("foo", StringUtils.join(Collections.singleton("foo"), 'x'));
    }

    @Test
    void testJoin_IterableString() {
        assertNull(StringUtils.join((Iterable<?>) null, null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(Arrays.asList(ARRAY_LIST), null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(Arrays.asList(ARRAY_LIST), ""));
        assertEquals("foo", StringUtils.join(Collections.singleton("foo"), "x"));
        assertEquals("foo", StringUtils.join(Collections.singleton("foo"), null));

        assertEquals("", StringUtils.join(Arrays.asList(NULL_ARRAY_LIST), null));

        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST), null));
        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST), ""));
        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST), SEPARATOR));

        assertEquals(TEXT_LIST, StringUtils.join(Arrays.asList(ARRAY_LIST), SEPARATOR));
    }

    @Test
    void testJoin_IteratorChar() {
        assertNull(StringUtils.join((Iterator<?>) null, ','));
        assertEquals(TEXT_LIST_CHAR, StringUtils.join(Arrays.asList(ARRAY_LIST).iterator(), SEPARATOR_CHAR));
        assertEquals("", StringUtils.join(Arrays.asList(NULL_ARRAY_LIST).iterator(), SEPARATOR_CHAR));
        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST).iterator(), SEPARATOR_CHAR));
        assertEquals("foo", StringUtils.join(Collections.singleton("foo").iterator(), 'x'));
        assertEquals("null", StringUtils.join(Arrays.asList(NULL_TO_STRING_LIST).iterator(), SEPARATOR_CHAR));
    }

    @Test
    void testJoin_IteratorString() {
        assertNull(StringUtils.join((Iterator<?>) null, null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(Arrays.asList(ARRAY_LIST).iterator(), null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(Arrays.asList(ARRAY_LIST).iterator(), ""));
        assertEquals("foo", StringUtils.join(Collections.singleton("foo").iterator(), "x"));
        assertEquals("foo", StringUtils.join(Collections.singleton("foo").iterator(), null));

        assertEquals("", StringUtils.join(Arrays.asList(NULL_ARRAY_LIST).iterator(), null));

        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST).iterator(), null));
        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST).iterator(), ""));
        assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST).iterator(), SEPARATOR));

        assertEquals(TEXT_LIST, StringUtils.join(Arrays.asList(ARRAY_LIST).iterator(), SEPARATOR));

        assertEquals("null", StringUtils.join(Arrays.asList(NULL_TO_STRING_LIST).iterator(), SEPARATOR));
    }

    @Test
    void testJoin_List_CharDelimiter() {
        assertEquals("/", StringUtils.join(MIXED_STRING_LIST, '/', 0, MIXED_STRING_LIST.size() - 1));
        assertEquals("foo", StringUtils.join(MIXED_TYPE_OBJECT_LIST, '/', 0, 1));
        assertEquals("foo/2", StringUtils.join(MIXED_TYPE_OBJECT_LIST, '/', 0, 2));
        assertEquals("2", StringUtils.join(MIXED_TYPE_OBJECT_LIST, '/', 1, 2));
        assertEquals("", StringUtils.join(MIXED_TYPE_OBJECT_LIST, '/', 2, 1));
        assertNull(null, StringUtils.join((List<?>) null, '/', 0, 1));
    }

    @Test
    void testJoin_List_EmptyDelimiter() {
        assertNull(StringUtils.join((List<String>) null, null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(STRING_LIST, null));
        assertEquals(TEXT_LIST_NOSEP, StringUtils.join(STRING_LIST, ""));

        assertEquals("", StringUtils.join(NULL_STRING_LIST, null));

        assertEquals("", StringUtils.join(EMPTY_STRING_LIST, null));
        assertEquals("", StringUtils.join(EMPTY_STRING_LIST, ""));

        assertEquals("", StringUtils.join(MIXED_STRING_LIST, "", 0, MIXED_STRING_LIST.size() - 1));
    }

    @ParameterizedTest
    @ValueSource(strings = {",", ";", Supplementary.CharU20000, Supplementary.CharU20001})
    void testJoin_List_NonEmptyDelimiter(final String delimiter) {
        assertEquals("", StringUtils.join(EMPTY_STRING_LIST, delimiter));

        assertEquals(String.join(delimiter, STRING_LIST), StringUtils.join(STRING_LIST, delimiter));
        assertEquals(delimiter + delimiter + "foo", StringUtils.join(MIXED_STRING_LIST, delimiter));
        assertEquals(String.join(delimiter, "foo", "2"), StringUtils.join(MIXED_TYPE_OBJECT_LIST, delimiter));

        assertEquals(delimiter, StringUtils.join(MIXED_STRING_LIST, delimiter, 0, MIXED_STRING_LIST.size() - 1));
        assertEquals("foo", StringUtils.join(MIXED_TYPE_OBJECT_LIST, delimiter, 0, 1));
        assertEquals(String.join(delimiter, "foo", "2"), StringUtils.join(MIXED_TYPE_OBJECT_LIST, delimiter, 0, 2));
        assertEquals("2", StringUtils.join(MIXED_TYPE_OBJECT_LIST, delimiter, 1, 2));
        assertEquals("", StringUtils.join(MIXED_TYPE_OBJECT_LIST, delimiter, 2, 1));
        assertNull(null, StringUtils.join((List<?>) null, delimiter, 0, 1));
    }

    @Test
    void testJoin_Objectarray() {
//        assertNull(StringUtils.join(null)); // generates warning
        assertNull(StringUtils.join((Object[]) null)); // equivalent explicit cast
        // test additional varargs calls
        assertEquals("", StringUtils.join()); // empty array
        assertEquals("", StringUtils.join((Object) null)); // => new Object[]{null}

        assertEquals("", StringUtils.join(EMPTY_ARRAY_LIST));
        assertEquals("", StringUtils.join(NULL_ARRAY_LIST));
        assertEquals("null", StringUtils.join(NULL_TO_STRING_LIST));
        assertEquals("abc", StringUtils.join("a", "b", "c"));
        assertEquals("a", StringUtils.join(null, "a", ""));
        assertEquals("foo", StringUtils.join(MIXED_ARRAY_LIST));
        assertEquals("foo2", StringUtils.join(MIXED_TYPE_LIST));
    }

    @Test
    void testJoin_Objects() {
        assertEquals("abc", StringUtils.join("a", "b", "c"));
        assertEquals("a", StringUtils.join(null, "", "a"));
        assertNull(StringUtils.join((Object[]) null));
    }

    @ParameterizedTest
    @ValueSource(strings = {",", ";", Supplementary.CharU20000, Supplementary.CharU20001})
    void testJoinWith(final String delimiter) {
        assertEquals("", StringUtils.joinWith(delimiter)); // empty array
        assertEquals("", StringUtils.joinWith(delimiter, (Object[]) NULL_ARRAY_LIST));
        assertEquals("null", StringUtils.joinWith(delimiter, NULL_TO_STRING_LIST)); // toString method prints 'null'

        assertEquals(String.join(delimiter, "a", "b", "c"), StringUtils.joinWith(delimiter, "a", "b", "c"));
        assertEquals(String.join(delimiter, "", "a", ""), StringUtils.joinWith(delimiter, null, "a", ""));
        assertEquals(String.join(delimiter, "", "a", ""), StringUtils.joinWith(delimiter, "", "a", ""));

        assertEquals("ab", StringUtils.joinWith(null, "a", "b"));
    }

    @Test
    void testJoinWithThrowsException() {
        assertIllegalArgumentException(() -> StringUtils.joinWith(",", (Object[]) null));
    }

    @Disabled
    @Test
    void testLang1593() {
        final int[] arr = {1, 2, 3, 4, 5, 6, 7};
        final String expected = StringUtils.join(arr, '-');
        final String actual = StringUtils.join(arr, "-");
        assertEquals(expected, actual);
    }

    @Test
    void testLang623() {
        assertEquals("t", StringUtils.replaceChars("\u00DE", '\u00DE', 't'));
        assertEquals("t", StringUtils.replaceChars("\u00FE", '\u00FE', 't'));
    }

    @Test
    void testLANG666() {
        assertEquals("12", StringUtils.stripEnd("120.00", ".0"));
        assertEquals("121", StringUtils.stripEnd("121.00", ".0"));
    }

    @Test
    void testLeftPad_StringInt() {
        assertNull(StringUtils.leftPad(null, 5));
        assertEquals("     ", StringUtils.leftPad("", 5));
        assertEquals("  abc", StringUtils.leftPad("abc", 5));
        assertEquals("abc", StringUtils.leftPad("abc", 2));
    }

    @Test
    void testLeftPad_StringIntChar() {
        assertNull(StringUtils.leftPad(null, 5, ' '));
        assertEquals("     ", StringUtils.leftPad("", 5, ' '));
        assertEquals("  abc", StringUtils.leftPad("abc", 5, ' '));
        assertEquals("xxabc", StringUtils.leftPad("abc", 5, 'x'));
        assertEquals("\uffff\uffffabc", StringUtils.leftPad("abc", 5, '\uffff'));
        assertEquals("abc", StringUtils.leftPad("abc", 2, ' '));
        final String str = StringUtils.leftPad("aaa", 10000, 'a');  // bigger than pad length
        assertEquals(10000, str.length());
        assertTrue(StringUtils.containsOnly(str, 'a'));
    }

    @Test
    void testLeftPad_StringIntString() {
        assertNull(StringUtils.leftPad(null, 5, "-+"));
        assertNull(StringUtils.leftPad(null, 5, null));
        assertEquals("     ", StringUtils.leftPad("", 5, " "));
        assertEquals("-+-+abc", StringUtils.leftPad("abc", 7, "-+"));
        assertEquals("-+~abc", StringUtils.leftPad("abc", 6, "-+~"));
        assertEquals("-+abc", StringUtils.leftPad("abc", 5, "-+~"));
        assertEquals("abc", StringUtils.leftPad("abc", 2, " "));
        assertEquals("abc", StringUtils.leftPad("abc", -1, " "));
        assertEquals("  abc", StringUtils.leftPad("abc", 5, null));
        assertEquals("  abc", StringUtils.leftPad("abc", 5, ""));
    }

    @Test
    void testLength_CharBuffer() {
        assertEquals(0, StringUtils.length(CharBuffer.wrap("")));
        assertEquals(1, StringUtils.length(CharBuffer.wrap("A")));
        assertEquals(1, StringUtils.length(CharBuffer.wrap(" ")));
        assertEquals(8, StringUtils.length(CharBuffer.wrap("ABCDEFGH")));
    }

    @Test
    void testLengthString() {
        assertEquals(0, StringUtils.length(null));
        assertEquals(0, StringUtils.length(""));
        assertEquals(0, StringUtils.length(StringUtils.EMPTY));
        assertEquals(1, StringUtils.length("A"));
        assertEquals(1, StringUtils.length(" "));
        assertEquals(8, StringUtils.length("ABCDEFGH"));
    }

    @Test
    void testLengthStringBuffer() {
        assertEquals(0, StringUtils.length(new StringBuffer("")));
        assertEquals(0, StringUtils.length(new StringBuffer(StringUtils.EMPTY)));
        assertEquals(1, StringUtils.length(new StringBuffer("A")));
        assertEquals(1, StringUtils.length(new StringBuffer(" ")));
        assertEquals(8, StringUtils.length(new StringBuffer("ABCDEFGH")));
    }

    @Test
    void testLengthStringBuilder() {
        assertEquals(0, StringUtils.length(new StringBuilder("")));
        assertEquals(0, StringUtils.length(new StringBuilder(StringUtils.EMPTY)));
        assertEquals(1, StringUtils.length(new StringBuilder("A")));
        assertEquals(1, StringUtils.length(new StringBuilder(" ")));
        assertEquals(8, StringUtils.length(new StringBuilder("ABCDEFGH")));
    }

    @Test
    void testLowerCase() {
        assertNull(StringUtils.lowerCase(null));
        assertNull(StringUtils.lowerCase(null, Locale.ENGLISH));
        assertEquals("foo test thing", StringUtils.lowerCase("fOo test THING"), "lowerCase(String) failed");
        assertEquals("", StringUtils.lowerCase(""), "lowerCase(empty-string) failed");
        assertEquals("foo test thing", StringUtils.lowerCase("fOo test THING", Locale.ENGLISH),
                "lowerCase(String, Locale) failed");
        assertEquals("", StringUtils.lowerCase("", Locale.ENGLISH), "lowerCase(empty-string, Locale) failed");
    }

    @Test
    void testNormalizeSpace() {
        // Java says a non-breaking whitespace is not a whitespace.
        assertFalse(Character.isWhitespace('\u00A0'));
        //
        assertNull(StringUtils.normalizeSpace(null));
        assertEquals("", StringUtils.normalizeSpace(""));
        assertEquals("", StringUtils.normalizeSpace(" "));
        assertEquals("", StringUtils.normalizeSpace("\t"));
        assertEquals("", StringUtils.normalizeSpace("\n"));
        assertEquals("", StringUtils.normalizeSpace("\u0009"));
        assertEquals("", StringUtils.normalizeSpace("\u000B"));
        assertEquals("", StringUtils.normalizeSpace("\u000C"));
        assertEquals("", StringUtils.normalizeSpace("\u001C"));
        assertEquals("", StringUtils.normalizeSpace("\u001D"));
        assertEquals("", StringUtils.normalizeSpace("\u001E"));
        assertEquals("", StringUtils.normalizeSpace("\u001F"));
        assertEquals("", StringUtils.normalizeSpace("\f"));
        assertEquals("", StringUtils.normalizeSpace("\r"));
        assertEquals("a", StringUtils.normalizeSpace("  a  "));
        assertEquals("a b c", StringUtils.normalizeSpace("  a  b   c  "));
        assertEquals("a b c", StringUtils.normalizeSpace("a\t\f\r  b\u000B   c\n"));
        assertEquals("a   b c", StringUtils.normalizeSpace("a\t\f\r  " + HARD_SPACE + HARD_SPACE + "b\u000B   c\n"));
        assertEquals("b", StringUtils.normalizeSpace("\u0000b"));
        assertEquals("b", StringUtils.normalizeSpace("b\u0000"));
    }

    @Test
    void testOverlay_StringStringIntInt() {
        assertNull(StringUtils.overlay(null, null, 2, 4));
        assertNull(StringUtils.overlay(null, null, -2, -4));

        assertEquals("", StringUtils.overlay("", null, 0, 0));
        assertEquals("", StringUtils.overlay("", "", 0, 0));
        assertEquals("zzzz", StringUtils.overlay("", "zzzz", 0, 0));
        assertEquals("zzzz", StringUtils.overlay("", "zzzz", 2, 4));
        assertEquals("zzzz", StringUtils.overlay("", "zzzz", -2, -4));

        assertEquals("abef", StringUtils.overlay("abcdef", null, 2, 4));
        assertEquals("abef", StringUtils.overlay("abcdef", null, 4, 2));
        assertEquals("abef", StringUtils.overlay("abcdef", "", 2, 4));
        assertEquals("abef", StringUtils.overlay("abcdef", "", 4, 2));
        assertEquals("abzzzzef", StringUtils.overlay("abcdef", "zzzz", 2, 4));
        assertEquals("abzzzzef", StringUtils.overlay("abcdef", "zzzz", 4, 2));

        assertEquals("zzzzef", StringUtils.overlay("abcdef", "zzzz", -1, 4));
        assertEquals("zzzzef", StringUtils.overlay("abcdef", "zzzz", 4, -1));
        assertEquals("zzzzabcdef", StringUtils.overlay("abcdef", "zzzz", -2, -1));
        assertEquals("zzzzabcdef", StringUtils.overlay("abcdef", "zzzz", -1, -2));
        assertEquals("abcdzzzz", StringUtils.overlay("abcdef", "zzzz", 4, 10));
        assertEquals("abcdzzzz", StringUtils.overlay("abcdef", "zzzz", 10, 4));
        assertEquals("abcdefzzzz", StringUtils.overlay("abcdef", "zzzz", 8, 10));
        assertEquals("abcdefzzzz", StringUtils.overlay("abcdef", "zzzz", 10, 8));
    }

    /**
     * Tests {@code prependIfMissing}.
     */
    @Test
    void testPrependIfMissing() {
        assertNull(StringUtils.prependIfMissing(null, null), "prependIfMissing(null,null)");
        assertEquals("abc", StringUtils.prependIfMissing("abc", null), "prependIfMissing(abc,null)");
        assertEquals("xyz", StringUtils.prependIfMissing("", "xyz"), "prependIfMissing(\"\",xyz)");
        assertEquals("xyzabc", StringUtils.prependIfMissing("abc", "xyz"), "prependIfMissing(abc,xyz)");
        assertEquals("xyzabc", StringUtils.prependIfMissing("xyzabc", "xyz"), "prependIfMissing(xyzabc,xyz)");
        assertEquals("xyzXYZabc", StringUtils.prependIfMissing("XYZabc", "xyz"), "prependIfMissing(XYZabc,xyz)");

        assertNull(StringUtils.prependIfMissing(null, null, (CharSequence[]) null), "prependIfMissing(null,null null)");
        assertEquals("abc", StringUtils.prependIfMissing("abc", null, (CharSequence[]) null), "prependIfMissing(abc,null,null)");
        assertEquals("xyz", StringUtils.prependIfMissing("", "xyz", (CharSequence[]) null), "prependIfMissing(\"\",xyz,null)");
        assertEquals("xyzabc", StringUtils.prependIfMissing("abc", "xyz", (CharSequence) null), "prependIfMissing(abc,xyz,{null})");
        assertEquals("abc", StringUtils.prependIfMissing("abc", "xyz", ""), "prependIfMissing(abc,xyz,\"\")");
        assertEquals("xyzabc", StringUtils.prependIfMissing("abc", "xyz", "mno"), "prependIfMissing(abc,xyz,mno)");
        assertEquals("xyzabc", StringUtils.prependIfMissing("xyzabc", "xyz", "mno"), "prependIfMissing(xyzabc,xyz,mno)");
        assertEquals("mnoabc", StringUtils.prependIfMissing("mnoabc", "xyz", "mno"), "prependIfMissing(mnoabc,xyz,mno)");
        assertEquals("xyzXYZabc", StringUtils.prependIfMissing("XYZabc", "xyz", "mno"), "prependIfMissing(XYZabc,xyz,mno)");
        assertEquals("xyzMNOabc", StringUtils.prependIfMissing("MNOabc", "xyz", "mno"), "prependIfMissing(MNOabc,xyz,mno)");
    }

    /**
     * Tests {@code prependIfMissingIgnoreCase}.
     */
    @Test
    void testPrependIfMissingIgnoreCase() {
        assertNull(StringUtils.prependIfMissingIgnoreCase(null, null), "prependIfMissingIgnoreCase(null,null)");
        assertEquals("abc", StringUtils.prependIfMissingIgnoreCase("abc", null), "prependIfMissingIgnoreCase(abc,null)");
        assertEquals("xyz", StringUtils.prependIfMissingIgnoreCase("", "xyz"), "prependIfMissingIgnoreCase(\"\",xyz)");
        assertEquals("xyzabc", StringUtils.prependIfMissingIgnoreCase("abc", "xyz"), "prependIfMissingIgnoreCase(abc,xyz)");
        assertEquals("xyzabc", StringUtils.prependIfMissingIgnoreCase("xyzabc", "xyz"), "prependIfMissingIgnoreCase(xyzabc,xyz)");
        assertEquals("XYZabc", StringUtils.prependIfMissingIgnoreCase("XYZabc", "xyz"), "prependIfMissingIgnoreCase(XYZabc,xyz)");

        assertNull(StringUtils.prependIfMissingIgnoreCase(null, null, (CharSequence[]) null), "prependIfMissingIgnoreCase(null,null null)");
        assertEquals("abc", StringUtils.prependIfMissingIgnoreCase("abc", null, (CharSequence[]) null), "prependIfMissingIgnoreCase(abc,null,null)");
        assertEquals("xyz", StringUtils.prependIfMissingIgnoreCase("", "xyz", (CharSequence[]) null), "prependIfMissingIgnoreCase(\"\",xyz,null)");
        assertEquals("xyzabc", StringUtils.prependIfMissingIgnoreCase("abc", "xyz", (CharSequence) null), "prependIfMissingIgnoreCase(abc,xyz,{null})");
        assertEquals("abc", StringUtils.prependIfMissingIgnoreCase("abc", "xyz", ""), "prependIfMissingIgnoreCase(abc,xyz,\"\")");
        assertEquals("xyzabc", StringUtils.prependIfMissingIgnoreCase("abc", "xyz", "mno"), "prependIfMissingIgnoreCase(abc,xyz,mno)");
        assertEquals("xyzabc", StringUtils.prependIfMissingIgnoreCase("xyzabc", "xyz", "mno"), "prependIfMissingIgnoreCase(xyzabc,xyz,mno)");
        assertEquals("mnoabc", StringUtils.prependIfMissingIgnoreCase("mnoabc", "xyz", "mno"), "prependIfMissingIgnoreCase(mnoabc,xyz,mno)");
        assertEquals("XYZabc", StringUtils.prependIfMissingIgnoreCase("XYZabc", "xyz", "mno"), "prependIfMissingIgnoreCase(XYZabc,xyz,mno)");
        assertEquals("MNOabc", StringUtils.prependIfMissingIgnoreCase("MNOabc", "xyz", "mno"), "prependIfMissingIgnoreCase(MNOabc,xyz,mno)");
    }

    @Test
    void testReCapitalize() {
        // reflection type of tests: Sentences.
        assertEquals(SENTENCE_UNCAP, StringUtils.uncapitalize(StringUtils.capitalize(SENTENCE_UNCAP)),
                "uncapitalize(capitalize(String)) failed");
        assertEquals(SENTENCE_CAP, StringUtils.capitalize(StringUtils.uncapitalize(SENTENCE_CAP)),
                "capitalize(uncapitalize(String)) failed");

        // reflection type of tests: One word.
        assertEquals(FOO_UNCAP, StringUtils.uncapitalize(StringUtils.capitalize(FOO_UNCAP)),
                "uncapitalize(capitalize(String)) failed");
        assertEquals(FOO_CAP, StringUtils.capitalize(StringUtils.uncapitalize(FOO_CAP)),
                "capitalize(uncapitalize(String)) failed");
    }

    @Test
    void testRemove_char() {
        // StringUtils.remove(null, *)       = null
        assertNull(StringUtils.remove(null, null));
        assertNull(StringUtils.remove(null, 'a'));

        // StringUtils.remove("", *)          = ""
        assertEquals("", StringUtils.remove("", null));
        assertEquals("", StringUtils.remove("", 'a'));

        // StringUtils.remove("queued", 'u') = "qeed"
        assertEquals("qeed", StringUtils.remove("queued", 'u'));

        // StringUtils.remove("queued", 'z') = "queued"
        assertEquals("queued", StringUtils.remove("queued", 'z'));
    }

    @Test
    void testRemove_String() {
        // StringUtils.remove(null, *)        = null
        assertNull(StringUtils.remove(null, null));
        assertNull(StringUtils.remove(null, ""));
        assertNull(StringUtils.remove(null, "a"));

        // StringUtils.remove("", *)          = ""
        assertEquals("", StringUtils.remove("", null));
        assertEquals("", StringUtils.remove("", ""));
        assertEquals("", StringUtils.remove("", "a"));

        // StringUtils.remove(*, null)        = *
        assertNull(StringUtils.remove(null, null));
        assertEquals("", StringUtils.remove("", null));
        assertEquals("a", StringUtils.remove("a", null));

        // StringUtils.remove(*, "")          = *
        assertNull(StringUtils.remove(null, ""));
        assertEquals("", StringUtils.remove("", ""));
        assertEquals("a", StringUtils.remove("a", ""));

        // StringUtils.remove("queued", "ue") = "qd"
        assertEquals("qd", StringUtils.remove("queued", "ue"));

        // StringUtils.remove("queued", "zz") = "queued"
        assertEquals("queued", StringUtils.remove("queued", "zz"));
    }

    @Test
    void testRemoveAll_StringString() {
        assertNull(StringUtils.removeAll(null, ""));
        assertEquals("any", StringUtils.removeAll("any", null));

        assertEquals("any", StringUtils.removeAll("any", ""));
        assertEquals("", StringUtils.removeAll("any", ".*"));
        assertEquals("", StringUtils.removeAll("any", ".+"));
        assertEquals("", StringUtils.removeAll("any", ".?"));

        assertEquals("A\nB", StringUtils.removeAll("A<__>\n<__>B", "<.*>"));
        assertEquals("AB", StringUtils.removeAll("A<__>\n<__>B", "(?s)<.*>"));
        assertEquals("ABC123", StringUtils.removeAll("ABCabc123abc", "[a-z]"));

        assertThrows(PatternSyntaxException.class, () -> StringUtils.removeAll("any", "{badRegexSyntax}"),
                "StringUtils.removeAll expecting PatternSyntaxException");
    }

    @Test
    void testRemoveEnd() {
        // StringUtils.removeEnd("", *)        = ""
        assertNull(StringUtils.removeEnd(null, null));
        assertNull(StringUtils.removeEnd(null, ""));
        assertNull(StringUtils.removeEnd(null, "a"));

        // StringUtils.removeEnd(*, null)      = *
        assertEquals(StringUtils.removeEnd("", null), "");
        assertEquals(StringUtils.removeEnd("", ""), "");
        assertEquals(StringUtils.removeEnd("", "a"), "");

        // All others:
        assertEquals(StringUtils.removeEnd("www.domain.com.", ".com"), "www.domain.com.");
        assertEquals(StringUtils.removeEnd("www.domain.com", ".com"), "www.domain");
        assertEquals(StringUtils.removeEnd("www.domain", ".com"), "www.domain");
        assertEquals(StringUtils.removeEnd("domain.com", ""), "domain.com");
        assertEquals(StringUtils.removeEnd("domain.com", null), "domain.com");
    }

    @Test
    void testRemoveEndIgnoreCase() {
        // StringUtils.removeEndIgnoreCase("", *)        = ""
        assertNull(StringUtils.removeEndIgnoreCase(null, null), "removeEndIgnoreCase(null, null)");
        assertNull(StringUtils.removeEndIgnoreCase(null, ""), "removeEndIgnoreCase(null, \"\")");
        assertNull(StringUtils.removeEndIgnoreCase(null, "a"), "removeEndIgnoreCase(null, \"a\")");

        // StringUtils.removeEnd(*, null)      = *
        assertEquals(StringUtils.removeEndIgnoreCase("", null), "", "removeEndIgnoreCase(\"\", null)");
        assertEquals(StringUtils.removeEndIgnoreCase("", ""), "", "removeEndIgnoreCase(\"\", \"\")");
        assertEquals(StringUtils.removeEndIgnoreCase("", "a"), "", "removeEndIgnoreCase(\"\", \"a\")");

        // All others:
        assertEquals(StringUtils.removeEndIgnoreCase("www.domain.com.", ".com"), "www.domain.com.", "removeEndIgnoreCase(\"www.domain.com.\", \".com\")");
        assertEquals(StringUtils.removeEndIgnoreCase("www.domain.com", ".com"), "www.domain", "removeEndIgnoreCase(\"www.domain.com\", \".com\")");
        assertEquals(StringUtils.removeEndIgnoreCase("www.domain", ".com"), "www.domain", "removeEndIgnoreCase(\"www.domain\", \".com\")");
        assertEquals(StringUtils.removeEndIgnoreCase("domain.com", ""), "domain.com", "removeEndIgnoreCase(\"domain.com\", \"\")");
        assertEquals(StringUtils.removeEndIgnoreCase("domain.com", null), "domain.com", "removeEndIgnoreCase(\"domain.com\", null)");

        // Case-insensitive:
        assertEquals(StringUtils.removeEndIgnoreCase("www.domain.com", ".COM"), "www.domain", "removeEndIgnoreCase(\"www.domain.com\", \".COM\")");
        assertEquals(StringUtils.removeEndIgnoreCase("www.domain.COM", ".com"), "www.domain", "removeEndIgnoreCase(\"www.domain.COM\", \".com\")");
    }

    @Test
    void testRemoveFirst_StringString() {
        assertNull(StringUtils.removeFirst(null, ""));
        assertEquals("any", StringUtils.removeFirst("any", null));

        assertEquals("any", StringUtils.removeFirst("any", ""));
        assertEquals("", StringUtils.removeFirst("any", ".*"));
        assertEquals("", StringUtils.removeFirst("any", ".+"));
        assertEquals("bc", StringUtils.removeFirst("abc", ".?"));

        assertEquals("A\n<__>B", StringUtils.removeFirst("A<__>\n<__>B", "<.*>"));
        assertEquals("AB", StringUtils.removeFirst("A<__>\n<__>B", "(?s)<.*>"));
        assertEquals("ABCbc123", StringUtils.removeFirst("ABCabc123", "[a-z]"));
        assertEquals("ABC123abc", StringUtils.removeFirst("ABCabc123abc", "[a-z]+"));

        assertThrows(PatternSyntaxException.class, () -> StringUtils.removeFirst("any", "{badRegexSyntax}"),
                "StringUtils.removeFirst expecting PatternSyntaxException");
    }

    @Test
    void testRemoveIgnoreCase_String() {
        // StringUtils.removeIgnoreCase(null, *) = null
        assertNull(StringUtils.removeIgnoreCase(null, null));
        assertNull(StringUtils.removeIgnoreCase(null, ""));
        assertNull(StringUtils.removeIgnoreCase(null, "a"));

        // StringUtils.removeIgnoreCase("", *) = ""
        assertEquals("", StringUtils.removeIgnoreCase("", null));
        assertEquals("", StringUtils.removeIgnoreCase("", ""));
        assertEquals("", StringUtils.removeIgnoreCase("", "a"));

        // StringUtils.removeIgnoreCase(*, null) = *
        assertNull(StringUtils.removeIgnoreCase(null, null));
        assertEquals("", StringUtils.removeIgnoreCase("", null));
        assertEquals("a", StringUtils.removeIgnoreCase("a", null));

        // StringUtils.removeIgnoreCase(*, "") = *
        assertNull(StringUtils.removeIgnoreCase(null, ""));
        assertEquals("", StringUtils.removeIgnoreCase("", ""));
        assertEquals("a", StringUtils.removeIgnoreCase("a", ""));

        // StringUtils.removeIgnoreCase("queued", "ue") = "qd"
        assertEquals("qd", StringUtils.removeIgnoreCase("queued", "ue"));

        // StringUtils.removeIgnoreCase("queued", "zz") = "queued"
        assertEquals("queued", StringUtils.removeIgnoreCase("queued", "zz"));

        // IgnoreCase
        // StringUtils.removeIgnoreCase("quEUed", "UE") = "qd"
        assertEquals("qd", StringUtils.removeIgnoreCase("quEUed", "UE"));

        // StringUtils.removeIgnoreCase("queued", "zZ") = "queued"
        assertEquals("queued", StringUtils.removeIgnoreCase("queued", "zZ"));

        // StringUtils.removeIgnoreCase("\u0130x", "x") = "\u0130"
        assertEquals("\u0130", StringUtils.removeIgnoreCase("\u0130x", "x"));

        // LANG-1453
        StringUtils.removeIgnoreCase("İa", "a");
    }

    @Test
    void testRemovePattern_StringString() {
        assertNull(StringUtils.removePattern(null, ""));
        assertEquals("any", StringUtils.removePattern("any", null));

        assertEquals("", StringUtils.removePattern("", ""));
        assertEquals("", StringUtils.removePattern("", ".*"));
        assertEquals("", StringUtils.removePattern("", ".+"));

        assertEquals("AB", StringUtils.removePattern("A<__>\n<__>B", "<.*>"));
        assertEquals("AB", StringUtils.removePattern("A<__>\\n<__>B", "<.*>"));
        assertEquals("", StringUtils.removePattern("<A>x\\ny</A>", "<A>.*</A>"));
        assertEquals("", StringUtils.removePattern("<A>\nxy\n</A>", "<A>.*</A>"));

        assertEquals("ABC123", StringUtils.removePattern("ABCabc123", "[a-z]"));
    }

    @Test
    void testRemoveStartChar() {
        // StringUtils.removeStart("", *)        = ""
        assertNull(StringUtils.removeStart(null, '\0'));
        assertNull(StringUtils.removeStart(null, 'a'));

        // StringUtils.removeStart(*, null)      = *
        assertEquals(StringUtils.removeStart("", '\0'), "");
        assertEquals(StringUtils.removeStart("", 'a'), "");

        // All others:
        assertEquals(StringUtils.removeStart("/path", '/'), "path");
        assertEquals(StringUtils.removeStart("path", '/'), "path");
        assertEquals(StringUtils.removeStart("path", '\0'), "path");
    }

    @Test
    void testRemoveStartIgnoreCase() {
        // StringUtils.removeStart("", *)        = ""
        assertNull(StringUtils.removeStartIgnoreCase(null, null), "removeStartIgnoreCase(null, null)");
        assertNull(StringUtils.removeStartIgnoreCase(null, ""), "removeStartIgnoreCase(null, \"\")");
        assertNull(StringUtils.removeStartIgnoreCase(null, "a"), "removeStartIgnoreCase(null, \"a\")");

        // StringUtils.removeStart(*, null)      = *
        assertEquals(StringUtils.removeStartIgnoreCase("", null), "", "removeStartIgnoreCase(\"\", null)");
        assertEquals(StringUtils.removeStartIgnoreCase("", ""), "", "removeStartIgnoreCase(\"\", \"\")");
        assertEquals(StringUtils.removeStartIgnoreCase("", "a"), "", "removeStartIgnoreCase(\"\", \"a\")");

        // All others:
        assertEquals(StringUtils.removeStartIgnoreCase("www.domain.com", "www."), "domain.com", "removeStartIgnoreCase(\"www.domain.com\", \"www.\")");
        assertEquals(StringUtils.removeStartIgnoreCase("domain.com", "www."), "domain.com", "removeStartIgnoreCase(\"domain.com\", \"www.\")");
        assertEquals(StringUtils.removeStartIgnoreCase("domain.com", ""), "domain.com", "removeStartIgnoreCase(\"domain.com\", \"\")");
        assertEquals(StringUtils.removeStartIgnoreCase("domain.com", null), "domain.com", "removeStartIgnoreCase(\"domain.com\", null)");

        // Case-insensitive:
        assertEquals(StringUtils.removeStartIgnoreCase("www.domain.com", "WWW."), "domain.com", "removeStartIgnoreCase(\"www.domain.com\", \"WWW.\")");
    }

    @Test
    void testRemoveStartString() {
        // StringUtils.removeStart("", *)        = ""
        assertNull(StringUtils.removeStart(null, null));
        assertNull(StringUtils.removeStart(null, ""));
        assertNull(StringUtils.removeStart(null, "a"));

        // StringUtils.removeStart(*, null)      = *
        assertEquals(StringUtils.removeStart("", null), "");
        assertEquals(StringUtils.removeStart("", ""), "");
        assertEquals(StringUtils.removeStart("", "a"), "");

        // All others:
        assertEquals(StringUtils.removeStart("www.domain.com", "www."), "domain.com");
        assertEquals(StringUtils.removeStart("domain.com", "www."), "domain.com");
        assertEquals(StringUtils.removeStart("domain.com", ""), "domain.com");
        assertEquals(StringUtils.removeStart("domain.com", null), "domain.com");
    }

    @Test
    void testRepeat_CharInt() {
        assertEquals("zzz", StringUtils.repeat('z', 3));
        assertEquals("", StringUtils.repeat('z', 0));
        assertEquals("", StringUtils.repeat('z', -2));
    }

    @Test
    void testRepeat_StringInt() {
        assertNull(StringUtils.repeat(null, 2));
        assertEquals("", StringUtils.repeat("ab", 0));
        assertEquals("", StringUtils.repeat("", 3));
        assertEquals("aaa", StringUtils.repeat("a", 3));
        assertEquals("", StringUtils.repeat("a", -2));
        assertEquals("ababab", StringUtils.repeat("ab", 3));
        assertEquals("abcabcabc", StringUtils.repeat("abc", 3));
        final String str = StringUtils.repeat("a", 10000);  // bigger than pad limit
        assertEquals(10000, str.length());
        assertTrue(StringUtils.containsOnly(str, 'a'));
        assertThrows(IllegalArgumentException.class, () -> StringUtils.repeat("aa", 1_073_741_824));
    }

    @Test
    void testRepeat_StringStringInt() {
        assertNull(StringUtils.repeat(null, null, 2));
        assertNull(StringUtils.repeat(null, "x", 2));
        assertEquals("", StringUtils.repeat("", null, 2));
        assertEquals("", StringUtils.repeat("ab", "", 0));
        assertEquals("", StringUtils.repeat("", "", 2));
        assertEquals("xx", StringUtils.repeat("", "x", 3));
        assertEquals("?, ?, ?", StringUtils.repeat("?", ", ", 3));
        assertThrows(IllegalArgumentException.class, () -> StringUtils.repeat("?", ", ", 1_073_741_824));
    }

    /**
     * Test method for 'StringUtils.replaceEach(String, String[], String[])'
     */
    @Test
    void testReplace_StringStringArrayStringArray() {
        // JAVADOC TESTS START
        assertNull(StringUtils.replaceEach(null, new String[]{"a"}, new String[]{"b"}));
        assertEquals(StringUtils.replaceEach("", new String[]{"a"}, new String[]{"b"}), "");
        assertEquals(StringUtils.replaceEach("aba", null, null), "aba");
        assertEquals(StringUtils.replaceEach("aba", new String[0], null), "aba");
        assertEquals(StringUtils.replaceEach("aba", null, new String[0]), "aba");
        assertEquals(StringUtils.replaceEach("aba", new String[]{"a"}, null), "aba");

        assertEquals(StringUtils.replaceEach("aba", new String[]{"a"}, new String[]{""}), "b");
        assertEquals(StringUtils.replaceEach("aba", new String[]{null}, new String[]{"a"}), "aba");
        assertEquals(StringUtils.replaceEach("abcde", new String[]{"ab", "d"}, new String[]{"w", "t"}), "wcte");
        assertEquals(StringUtils.replaceEach("abcde", new String[]{"ab", "d"}, new String[]{"d", "t"}), "dcte");
        // JAVADOC TESTS END

        assertEquals("bcc", StringUtils.replaceEach("abc", new String[]{"a", "b"}, new String[]{"b", "c"}));
        assertEquals("q651.506bera", StringUtils.replaceEach("d216.102oren",
                new String[]{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n",
                        "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "A", "B", "C", "D",
                        "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
                        "U", "V", "W", "X", "Y", "Z", "1", "2", "3", "4", "5", "6", "7", "8", "9"},
                new String[]{"n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "a",
                        "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "N", "O", "P", "Q",
                        "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "A", "B", "C", "D", "E", "F", "G",
                        "H", "I", "J", "K", "L", "M", "5", "6", "7", "8", "9", "1", "2", "3", "4"}));

        // Test null safety inside arrays - LANG-552
        assertEquals(StringUtils.replaceEach("aba", new String[]{"a"}, new String[]{null}), "aba");
        assertEquals(StringUtils.replaceEach("aba", new String[]{"a", "b"}, new String[]{"c", null}), "cbc");

        assertIllegalArgumentException(() -> StringUtils.replaceEach("abba", new String[] { "a" }, new String[] { "b", "a" }),
                "StringUtils.replaceEach(String, String[], String[]) expecting IllegalArgumentException");
    }

    /**
     * Test method for 'StringUtils.replaceEachRepeatedly(String, String[], String[])'
     */
    @Test
    void testReplace_StringStringArrayStringArrayBoolean() {
        //JAVADOC TESTS START
        assertNull(StringUtils.replaceEachRepeatedly(null, new String[]{"a"}, new String[]{"b"}));
        assertEquals("", StringUtils.replaceEachRepeatedly("", new String[]{"a"}, new String[]{"b"}));
        assertEquals("aba", StringUtils.replaceEachRepeatedly("aba", null, null));
        assertEquals("aba", StringUtils.replaceEachRepeatedly("aba", new String[0], null));
        assertEquals("aba", StringUtils.replaceEachRepeatedly("aba", null, new String[0]));
        assertEquals("aba", StringUtils.replaceEachRepeatedly("aba", new String[0], null));

        assertEquals("b", StringUtils.replaceEachRepeatedly("aba", new String[]{"a"}, new String[]{""}));
        assertEquals("aba", StringUtils.replaceEachRepeatedly("aba", new String[]{null}, new String[]{"a"}));
        assertEquals("wcte", StringUtils.replaceEachRepeatedly("abcde", new String[]{"ab", "d"}, new String[]{"w", "t"}));
        assertEquals("tcte", StringUtils.replaceEachRepeatedly("abcde", new String[]{"ab", "d"}, new String[]{"d", "t"}));

        // Test recursive replacement - LANG-1528 & LANG-1753
        assertEquals("blaan", StringUtils.replaceEachRepeatedly("blllaan", new String[]{"llaan"}, new String[]{"laan"}));
        assertEquals("blaan", StringUtils.replaceEachRepeatedly("bllllaan", new String[]{"llaan"}, new String[]{"laan"}));

        // Test default TTL for smaller search lists. 32 characters reduced to 16, then 8, 4, 2, 1.
        assertEquals("a", StringUtils.replaceEachRepeatedly("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
                new String[]{"aa"}, new String[]{"a"}));

        // Test default TTL exceeded. 33 characters reduced to 17, then 9, 5, 3, 2 (still found).
        assertThrows(IllegalStateException.class,
                () -> StringUtils.replaceEachRepeatedly("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", new String[] { "aa" }, new String[] { "a" }),
                "Cannot be resolved within the default time-to-live limit");
        // Test larger TTL for larger search lists. Replace repeatedly until there are no more possible replacements.
        assertEquals("000000000", StringUtils.replaceEachRepeatedly("aA0aA0aA0",
                new String[]{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n",
                        "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "A", "B", "C", "D",
                        "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
                        "U", "V", "W", "X", "Y", "Z", "1", "2", "3", "4", "5", "6", "7", "8", "9"},
                new String[]{"b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o",
                        "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "A", "B", "C", "D", "E",
                        "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U",
                        "V", "W", "X", "Y", "Z", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"}));

        // Test long infinite cycle: a -> b -> ... -> 9 -> 0 -> a -> b -> ...
        assertThrows(IllegalStateException.class,
                () -> StringUtils.replaceEachRepeatedly("a",
                    new String[]{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n",
                            "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "A", "B", "C", "D",
                            "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
                            "U", "V", "W", "X", "Y", "Z", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"},
                    new String[]{"b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o",
                            "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "A", "B", "C", "D", "E",
                            "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U",
                            "V", "W", "X", "Y", "Z", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0", "a"}),
                "Should be a circular reference");

        assertThrows(IllegalStateException.class,
                () -> StringUtils.replaceEachRepeatedly("%{key1}",
                    new String[] {"%{key1}", "%{key2}", "%{key3}"},
                    new String[] {"Key1 %{key2}", "Key2 %{key3}", "Key3 %{key1}"}),
                "Should be a circular reference");

        assertThrows(IllegalStateException.class,
                () -> StringUtils.replaceEachRepeatedly("abcde", new String[]{"ab", "d"}, new String[]{"d", "ab"}),
                "Should be a circular reference");

        //JAVADOC TESTS END
    }

    @Test
    void testReplace_StringStringString() {
        assertNull(StringUtils.replace(null, null, null));
        assertNull(StringUtils.replace(null, null, "any"));
        assertNull(StringUtils.replace(null, "any", null));
        assertNull(StringUtils.replace(null, "any", "any"));

        assertEquals("", StringUtils.replace("", null, null));
        assertEquals("", StringUtils.replace("", null, "any"));
        assertEquals("", StringUtils.replace("", "any", null));
        assertEquals("", StringUtils.replace("", "any", "any"));

        assertEquals("FOO", StringUtils.replace("FOO", "", "any"));
        assertEquals("FOO", StringUtils.replace("FOO", null, "any"));
        assertEquals("FOO", StringUtils.replace("FOO", "F", null));
        assertEquals("FOO", StringUtils.replace("FOO", null, null));

        assertEquals("", StringUtils.replace("foofoofoo", "foo", ""));
        assertEquals("barbarbar", StringUtils.replace("foofoofoo", "foo", "bar"));
        assertEquals("farfarfar", StringUtils.replace("foofoofoo", "oo", "ar"));
    }

    @Test
    void testReplace_StringStringStringInt() {
        assertNull(StringUtils.replace(null, null, null, 2));
        assertNull(StringUtils.replace(null, null, "any", 2));
        assertNull(StringUtils.replace(null, "any", null, 2));
        assertNull(StringUtils.replace(null, "any", "any", 2));

        assertEquals("", StringUtils.replace("", null, null, 2));
        assertEquals("", StringUtils.replace("", null, "any", 2));
        assertEquals("", StringUtils.replace("", "any", null, 2));
        assertEquals("", StringUtils.replace("", "any", "any", 2));

        final String str = new String(new char[]{'o', 'o', 'f', 'o', 'o'});
        assertSame(str, StringUtils.replace(str, "x", "", -1));

        assertEquals("f", StringUtils.replace("oofoo", "o", "", -1));
        assertEquals("oofoo", StringUtils.replace("oofoo", "o", "", 0));
        assertEquals("ofoo", StringUtils.replace("oofoo", "o", "", 1));
        assertEquals("foo", StringUtils.replace("oofoo", "o", "", 2));
        assertEquals("fo", StringUtils.replace("oofoo", "o", "", 3));
        assertEquals("f", StringUtils.replace("oofoo", "o", "", 4));

        assertEquals("f", StringUtils.replace("oofoo", "o", "", -5));
        assertEquals("f", StringUtils.replace("oofoo", "o", "", 1000));
    }

    @Test
    void testReplaceAll_StringStringString() {
        assertNull(StringUtils.replaceAll(null, "", ""));

        assertEquals("any", StringUtils.replaceAll("any", null, ""));
        assertEquals("any", StringUtils.replaceAll("any", "", null));

        assertEquals("zzz", StringUtils.replaceAll("", "", "zzz"));
        assertEquals("zzz", StringUtils.replaceAll("", ".*", "zzz"));
        assertEquals("", StringUtils.replaceAll("", ".+", "zzz"));
        assertEquals("ZZaZZbZZcZZ", StringUtils.replaceAll("abc", "", "ZZ"));

        assertEquals("z\nz", StringUtils.replaceAll("<__>\n<__>", "<.*>", "z"));
        assertEquals("z", StringUtils.replaceAll("<__>\n<__>", "(?s)<.*>", "z"));

        assertEquals("ABC___123", StringUtils.replaceAll("ABCabc123", "[a-z]", "_"));
        assertEquals("ABC_123", StringUtils.replaceAll("ABCabc123", "[^A-Z0-9]+", "_"));
        assertEquals("ABC123", StringUtils.replaceAll("ABCabc123", "[^A-Z0-9]+", ""));
        assertEquals("Lorem_ipsum_dolor_sit",
                     StringUtils.replaceAll("Lorem ipsum  dolor   sit", "( +)([a-z]+)", "_$2"));

        assertThrows(PatternSyntaxException.class, () -> StringUtils.replaceAll("any", "{badRegexSyntax}", ""),
                "StringUtils.replaceAll expecting PatternSyntaxException");
    }

    @Test
    void testReplaceChars_StringCharChar() {
        assertNull(StringUtils.replaceChars(null, 'b', 'z'));
        assertEquals("", StringUtils.replaceChars("", 'b', 'z'));
        assertEquals("azcza", StringUtils.replaceChars("abcba", 'b', 'z'));
        assertEquals("abcba", StringUtils.replaceChars("abcba", 'x', 'z'));
    }

    @Test
    void testReplaceChars_StringStringString() {
        assertNull(StringUtils.replaceChars(null, null, null));
        assertNull(StringUtils.replaceChars(null, "", null));
        assertNull(StringUtils.replaceChars(null, "a", null));
        assertNull(StringUtils.replaceChars(null, null, ""));
        assertNull(StringUtils.replaceChars(null, null, "x"));

        assertEquals("", StringUtils.replaceChars("", null, null));
        assertEquals("", StringUtils.replaceChars("", "", null));
        assertEquals("", StringUtils.replaceChars("", "a", null));
        assertEquals("", StringUtils.replaceChars("", null, ""));
        assertEquals("", StringUtils.replaceChars("", null, "x"));

        assertEquals("abc", StringUtils.replaceChars("abc", null, null));
        assertEquals("abc", StringUtils.replaceChars("abc", null, ""));
        assertEquals("abc", StringUtils.replaceChars("abc", null, "x"));

        assertEquals("abc", StringUtils.replaceChars("abc", "", null));
        assertEquals("abc", StringUtils.replaceChars("abc", "", ""));
        assertEquals("abc", StringUtils.replaceChars("abc", "", "x"));

        assertEquals("ac", StringUtils.replaceChars("abc", "b", null));
        assertEquals("ac", StringUtils.replaceChars("abc", "b", ""));
        assertEquals("axc", StringUtils.replaceChars("abc", "b", "x"));

        assertEquals("ayzya", StringUtils.replaceChars("abcba", "bc", "yz"));
        assertEquals("ayya", StringUtils.replaceChars("abcba", "bc", "y"));
        assertEquals("ayzya", StringUtils.replaceChars("abcba", "bc", "yzx"));

        assertEquals("abcba", StringUtils.replaceChars("abcba", "z", "w"));
        assertSame("abcba", StringUtils.replaceChars("abcba", "z", "w"));

        // Javadoc examples:
        assertEquals("jelly", StringUtils.replaceChars("hello", "ho", "jy"));
        assertEquals("ayzya", StringUtils.replaceChars("abcba", "bc", "yz"));
        assertEquals("ayya", StringUtils.replaceChars("abcba", "bc", "y"));
        assertEquals("ayzya", StringUtils.replaceChars("abcba", "bc", "yzx"));

        // From https://issues.apache.org/bugzilla/show_bug.cgi?id=25454
        assertEquals("bcc", StringUtils.replaceChars("abc", "ab", "bc"));
        assertEquals("q651.506bera", StringUtils.replaceChars("d216.102oren",
                "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ123456789",
                "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM567891234"));
    }

    @Test
    void testReplaceFirst_StringStringString() {
        assertNull(StringUtils.replaceFirst(null, "", ""));

        assertEquals("any", StringUtils.replaceFirst("any", null, ""));
        assertEquals("any", StringUtils.replaceFirst("any", "", null));

        assertEquals("zzz", StringUtils.replaceFirst("", "", "zzz"));
        assertEquals("zzz", StringUtils.replaceFirst("", ".*", "zzz"));
        assertEquals("", StringUtils.replaceFirst("", ".+", "zzz"));
        assertEquals("ZZabc", StringUtils.replaceFirst("abc", "", "ZZ"));

        assertEquals("z\n<__>", StringUtils.replaceFirst("<__>\n<__>", "<.*>", "z"));
        assertEquals("z", StringUtils.replaceFirst("<__>\n<__>", "(?s)<.*>", "z"));

        assertEquals("ABC_bc123", StringUtils.replaceFirst("ABCabc123", "[a-z]", "_"));
        assertEquals("ABC_123abc", StringUtils.replaceFirst("ABCabc123abc", "[^A-Z0-9]+", "_"));
        assertEquals("ABC123abc", StringUtils.replaceFirst("ABCabc123abc", "[^A-Z0-9]+", ""));
        assertEquals("Lorem_ipsum  dolor   sit",
                     StringUtils.replaceFirst("Lorem ipsum  dolor   sit", "( +)([a-z]+)", "_$2"));

        assertThrows(PatternSyntaxException.class, () -> StringUtils.replaceFirst("any", "{badRegexSyntax}", ""),
                "StringUtils.replaceFirst expecting PatternSyntaxException");
    }

    @Test
    void testReplaceIgnoreCase_StringStringString() {
        assertNull(StringUtils.replaceIgnoreCase(null, null, null));
        assertNull(StringUtils.replaceIgnoreCase(null, null, "any"));
        assertNull(StringUtils.replaceIgnoreCase(null, "any", null));
        assertNull(StringUtils.replaceIgnoreCase(null, "any", "any"));

        assertEquals("", StringUtils.replaceIgnoreCase("", null, null));
        assertEquals("", StringUtils.replaceIgnoreCase("", null, "any"));
        assertEquals("", StringUtils.replaceIgnoreCase("", "any", null));
        assertEquals("", StringUtils.replaceIgnoreCase("", "any", "any"));

        assertEquals("FOO", StringUtils.replaceIgnoreCase("FOO", "", "any"));
        assertEquals("FOO", StringUtils.replaceIgnoreCase("FOO", null, "any"));
        assertEquals("FOO", StringUtils.replaceIgnoreCase("FOO", "F", null));
        assertEquals("FOO", StringUtils.replaceIgnoreCase("FOO", null, null));

        assertEquals("", StringUtils.replaceIgnoreCase("foofoofoo", "foo", ""));
        assertEquals("barbarbar", StringUtils.replaceIgnoreCase("foofoofoo", "foo", "bar"));
        assertEquals("farfarfar", StringUtils.replaceIgnoreCase("foofoofoo", "oo", "ar"));

        // IgnoreCase
        assertEquals("", StringUtils.replaceIgnoreCase("foofoofoo", "FOO", ""));
        assertEquals("barbarbar", StringUtils.replaceIgnoreCase("fooFOOfoo", "foo", "bar"));
        assertEquals("farfarfar", StringUtils.replaceIgnoreCase("foofOOfoo", "OO", "ar"));
    }

    @Test
    void testReplaceIgnoreCase_StringStringStringInt() {
        assertNull(StringUtils.replaceIgnoreCase(null, null, null, 2));
        assertNull(StringUtils.replaceIgnoreCase(null, null, "any", 2));
        assertNull(StringUtils.replaceIgnoreCase(null, "any", null, 2));
        assertNull(StringUtils.replaceIgnoreCase(null, "any", "any", 2));

        assertEquals("", StringUtils.replaceIgnoreCase("", null, null, 2));
        assertEquals("", StringUtils.replaceIgnoreCase("", null, "any", 2));
        assertEquals("", StringUtils.replaceIgnoreCase("", "any", null, 2));
        assertEquals("", StringUtils.replaceIgnoreCase("", "any", "any", 2));

        final String str = new String(new char[] { 'o', 'o', 'f', 'o', 'o' });
        assertSame(str, StringUtils.replaceIgnoreCase(str, "x", "", -1));

        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "o", "", -1));
        assertEquals("oofoo", StringUtils.replaceIgnoreCase("oofoo", "o", "", 0));
        assertEquals("ofoo", StringUtils.replaceIgnoreCase("oofoo", "o", "", 1));
        assertEquals("foo", StringUtils.replaceIgnoreCase("oofoo", "o", "", 2));
        assertEquals("fo", StringUtils.replaceIgnoreCase("oofoo", "o", "", 3));
        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "o", "", 4));

        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "o", "", -5));
        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "o", "", 1000));

        // IgnoreCase
        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "O", "", -1));
        assertEquals("oofoo", StringUtils.replaceIgnoreCase("oofoo", "O", "", 0));
        assertEquals("ofoo", StringUtils.replaceIgnoreCase("oofoo", "O", "", 1));
        assertEquals("foo", StringUtils.replaceIgnoreCase("oofoo", "O", "", 2));
        assertEquals("fo", StringUtils.replaceIgnoreCase("oofoo", "O", "", 3));
        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "O", "", 4));

        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "O", "", -5));
        assertEquals("f", StringUtils.replaceIgnoreCase("oofoo", "O", "", 1000));
    }

    @Test
    void testReplaceOnce_StringStringString() {
        assertNull(StringUtils.replaceOnce(null, null, null));
        assertNull(StringUtils.replaceOnce(null, null, "any"));
        assertNull(StringUtils.replaceOnce(null, "any", null));
        assertNull(StringUtils.replaceOnce(null, "any", "any"));

        assertEquals("", StringUtils.replaceOnce("", null, null));
        assertEquals("", StringUtils.replaceOnce("", null, "any"));
        assertEquals("", StringUtils.replaceOnce("", "any", null));
        assertEquals("", StringUtils.replaceOnce("", "any", "any"));

        assertEquals("FOO", StringUtils.replaceOnce("FOO", "", "any"));
        assertEquals("FOO", StringUtils.replaceOnce("FOO", null, "any"));
        assertEquals("FOO", StringUtils.replaceOnce("FOO", "F", null));
        assertEquals("FOO", StringUtils.replaceOnce("FOO", null, null));

        assertEquals("foofoo", StringUtils.replaceOnce("foofoofoo", "foo", ""));
    }

    @Test
    void testReplaceOnceIgnoreCase_StringStringString() {
        assertNull(StringUtils.replaceOnceIgnoreCase(null, null, null));
        assertNull(StringUtils.replaceOnceIgnoreCase(null, null, "any"));
        assertNull(StringUtils.replaceOnceIgnoreCase(null, "any", null));
        assertNull(StringUtils.replaceOnceIgnoreCase(null, "any", "any"));

        assertEquals("", StringUtils.replaceOnceIgnoreCase("", null, null));
        assertEquals("", StringUtils.replaceOnceIgnoreCase("", null, "any"));
        assertEquals("", StringUtils.replaceOnceIgnoreCase("", "any", null));
        assertEquals("", StringUtils.replaceOnceIgnoreCase("", "any", "any"));

        assertEquals("FOO", StringUtils.replaceOnceIgnoreCase("FOO", "", "any"));
        assertEquals("FOO", StringUtils.replaceOnceIgnoreCase("FOO", null, "any"));
        assertEquals("FOO", StringUtils.replaceOnceIgnoreCase("FOO", "F", null));
        assertEquals("FOO", StringUtils.replaceOnceIgnoreCase("FOO", null, null));

        assertEquals("foofoo", StringUtils.replaceOnceIgnoreCase("foofoofoo", "foo", ""));

        // Ignore Case
        assertEquals("Foofoo", StringUtils.replaceOnceIgnoreCase("FoOFoofoo", "foo", ""));
    }

    @Test
    void testReplacePattern_StringStringString() {
        assertNull(StringUtils.replacePattern(null, "", ""));
        assertEquals("any", StringUtils.replacePattern("any", null, ""));
        assertEquals("any", StringUtils.replacePattern("any", "", null));

        assertEquals("zzz", StringUtils.replacePattern("", "", "zzz"));
        assertEquals("zzz", StringUtils.replacePattern("", ".*", "zzz"));
        assertEquals("", StringUtils.replacePattern("", ".+", "zzz"));

        assertEquals("z", StringUtils.replacePattern("<__>\n<__>", "<.*>", "z"));
        assertEquals("z", StringUtils.replacePattern("<__>\\n<__>", "<.*>", "z"));
        assertEquals("X", StringUtils.replacePattern("<A>\nxy\n</A>", "<A>.*</A>", "X"));

        assertEquals("ABC___123", StringUtils.replacePattern("ABCabc123", "[a-z]", "_"));
        assertEquals("ABC_123", StringUtils.replacePattern("ABCabc123", "[^A-Z0-9]+", "_"));
        assertEquals("ABC123", StringUtils.replacePattern("ABCabc123", "[^A-Z0-9]+", ""));
        assertEquals("Lorem_ipsum_dolor_sit",
                     StringUtils.replacePattern("Lorem ipsum  dolor   sit", "( +)([a-z]+)", "_$2"));
    }

    @Test
    void testReverse_String() {
        assertNull(StringUtils.reverse(null));
        assertEquals("", StringUtils.reverse(""));
        assertEquals("sdrawkcab", StringUtils.reverse("backwards"));
    }

    @Test
    void testReverseDelimited_StringChar() {
        assertNull(StringUtils.reverseDelimited(null, '.'));
        assertEquals("", StringUtils.reverseDelimited("", '.'));
        assertEquals("c.b.a", StringUtils.reverseDelimited("a.b.c", '.'));
        assertEquals("a b c", StringUtils.reverseDelimited("a b c", '.'));
        assertEquals("", StringUtils.reverseDelimited("", '.'));
    }

    @Test
    void testRightPad_StringInt() {
        assertNull(StringUtils.rightPad(null, 5));
        assertEquals("     ", StringUtils.rightPad("", 5));
        assertEquals("abc  ", StringUtils.rightPad("abc", 5));
        assertEquals("abc", StringUtils.rightPad("abc", 2));
        assertEquals("abc", StringUtils.rightPad("abc", -1));
    }

    @Test
    void testRightPad_StringIntChar() {
        assertNull(StringUtils.rightPad(null, 5, ' '));
        assertEquals("     ", StringUtils.rightPad("", 5, ' '));
        assertEquals("abc  ", StringUtils.rightPad("abc", 5, ' '));
        assertEquals("abc", StringUtils.rightPad("abc", 2, ' '));
        assertEquals("abc", StringUtils.rightPad("abc", -1, ' '));
        assertEquals("abcxx", StringUtils.rightPad("abc", 5, 'x'));
        final String str = StringUtils.rightPad("aaa", 10000, 'a');  // bigger than pad length
        assertEquals(10000, str.length());
        assertTrue(StringUtils.containsOnly(str, 'a'));
    }

    @Test
    void testRightPad_StringIntString() {
        assertNull(StringUtils.rightPad(null, 5, "-+"));
        assertEquals("     ", StringUtils.rightPad("", 5, " "));
        assertNull(StringUtils.rightPad(null, 8, null));
        assertEquals("abc-+-+", StringUtils.rightPad("abc", 7, "-+"));
        assertEquals("abc-+~", StringUtils.rightPad("abc", 6, "-+~"));
        assertEquals("abc-+", StringUtils.rightPad("abc", 5, "-+~"));
        assertEquals("abc", StringUtils.rightPad("abc", 2, " "));
        assertEquals("abc", StringUtils.rightPad("abc", -1, " "));
        assertEquals("abc  ", StringUtils.rightPad("abc", 5, null));
        assertEquals("abc  ", StringUtils.rightPad("abc", 5, ""));
    }

    @Test
    void testRotate_StringInt() {
        assertNull(StringUtils.rotate(null, 1));
        assertEquals("", StringUtils.rotate("", 1));
        assertEquals("abcdefg", StringUtils.rotate("abcdefg", 0));
        assertEquals("fgabcde", StringUtils.rotate("abcdefg", 2));
        assertEquals("cdefgab", StringUtils.rotate("abcdefg", -2));
        assertEquals("abcdefg", StringUtils.rotate("abcdefg", 7));
        assertEquals("abcdefg", StringUtils.rotate("abcdefg", -7));
        assertEquals("fgabcde", StringUtils.rotate("abcdefg", 9));
        assertEquals("cdefgab", StringUtils.rotate("abcdefg", -9));
        assertEquals("efgabcd", StringUtils.rotate("abcdefg", 17));
        assertEquals("defgabc", StringUtils.rotate("abcdefg", -17));
    }

    @Test
    void testSplit_String() {
        assertNull(StringUtils.split(null));
        assertEquals(0, StringUtils.split("").length);

        String str = "a b  .c";
        String[] res = StringUtils.split(str);
        assertEquals(3, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals(".c", res[2]);

        str = " a ";
        res = StringUtils.split(str);
        assertEquals(1, res.length);
        assertEquals("a", res[0]);

        str = "a" + WHITESPACE + "b" + NON_WHITESPACE + "c";
        res = StringUtils.split(str);
        assertEquals(2, res.length);
        assertEquals("a", res[0]);
        assertEquals("b" + NON_WHITESPACE + "c", res[1]);
    }

    @Test
    void testSplit_StringChar() {
        assertNull(StringUtils.split(null, '.'));
        assertEquals(0, StringUtils.split("", '.').length);

        String str = "a.b.. c";
        String[] res = StringUtils.split(str, '.');
        assertEquals(3, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals(" c", res[2]);

        str = ".a.";
        res = StringUtils.split(str, '.');
        assertEquals(1, res.length);
        assertEquals("a", res[0]);

        str = "a b c";
        res = StringUtils.split(str, ' ');
        assertEquals(3, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals("c", res[2]);
    }

    @Test
    void testSplit_StringString_StringStringInt() {
        assertNull(StringUtils.split(null, "."));
        assertNull(StringUtils.split(null, ".", 3));

        assertEquals(0, StringUtils.split("", ".").length);
        assertEquals(0, StringUtils.split("", ".", 3).length);

        innerTestSplit('.', ".", ' ');
        innerTestSplit('.', ".", ',');
        innerTestSplit('.', ".,", 'x');
        for (int i = 0; i < WHITESPACE.length(); i++) {
            for (int j = 0; j < NON_WHITESPACE.length(); j++) {
                innerTestSplit(WHITESPACE.charAt(i), null, NON_WHITESPACE.charAt(j));
                innerTestSplit(WHITESPACE.charAt(i), String.valueOf(WHITESPACE.charAt(i)), NON_WHITESPACE.charAt(j));
            }
        }

        String[] results;
        final String[] expectedResults = {"ab", "de fg"};
        results = StringUtils.split("ab   de fg", null, 2);
        assertEquals(expectedResults.length, results.length);
        for (int i = 0; i < expectedResults.length; i++) {
            assertEquals(expectedResults[i], results[i]);
        }

        final String[] expectedResults2 = {"ab", "cd:ef"};
        results = StringUtils.split("ab:cd:ef", ":", 2);
        assertEquals(expectedResults2.length, results.length);
        for (int i = 0; i < expectedResults2.length; i++) {
            assertEquals(expectedResults2[i], results[i]);
        }
    }

    @Test
    void testSplitByCharacterType() {
        assertNull(StringUtils.splitByCharacterType(null));
        assertEquals(0, StringUtils.splitByCharacterType("").length);

        assertTrue(Objects.deepEquals(new String[]{"ab", " ", "de", " ",
                "fg"}, StringUtils.splitByCharacterType("ab de fg")));

        assertTrue(Objects.deepEquals(new String[]{"ab", "   ", "de", " ",
                "fg"}, StringUtils.splitByCharacterType("ab   de fg")));

        assertTrue(Objects.deepEquals(new String[]{"ab", ":", "cd", ":",
                "ef"}, StringUtils.splitByCharacterType("ab:cd:ef")));

        assertTrue(Objects.deepEquals(new String[]{"number", "5"},
                StringUtils.splitByCharacterType("number5")));

        assertTrue(Objects.deepEquals(new String[]{"foo", "B", "ar"},
                StringUtils.splitByCharacterType("fooBar")));

        assertTrue(Objects.deepEquals(new String[]{"foo", "200", "B", "ar"},
                StringUtils.splitByCharacterType("foo200Bar")));

        assertTrue(Objects.deepEquals(new String[]{"ASFR", "ules"},
                StringUtils.splitByCharacterType("ASFRules")));

        // Supplementary code points are classified by their own type, not split apart as surrogates.
        // U+1D400 MATHEMATICAL BOLD CAPITAL A is an upper-case letter, like ASCII 'A'.
        final String boldA = new String(Character.toChars(0x1D400));
        // U+1D7D3 MATHEMATICAL BOLD DIGIT FIVE is a decimal digit, like ASCII '5'.
        final String boldFive = new String(Character.toChars(0x1D7D3));
        assertTrue(Objects.deepEquals(new String[]{"A" + boldA},
                StringUtils.splitByCharacterType("A" + boldA)));
        assertTrue(Objects.deepEquals(new String[]{"5" + boldFive},
                StringUtils.splitByCharacterType("5" + boldFive)));
        assertTrue(Objects.deepEquals(new String[]{boldA, "5" + boldFive, "z"},
                StringUtils.splitByCharacterType(boldA + "5" + boldFive + "z")));
    }

    @Test
    void testSplitByCharacterTypeCamelCase() {
        assertNull(StringUtils.splitByCharacterTypeCamelCase(null));
        assertEquals(0, StringUtils.splitByCharacterTypeCamelCase("").length);

        assertTrue(Objects.deepEquals(new String[]{"ab", " ", "de", " ",
                "fg"}, StringUtils.splitByCharacterTypeCamelCase("ab de fg")));

        assertTrue(Objects.deepEquals(new String[]{"ab", "   ", "de", " ",
                "fg"}, StringUtils.splitByCharacterTypeCamelCase("ab   de fg")));

        assertTrue(Objects.deepEquals(new String[]{"ab", ":", "cd", ":",
                "ef"}, StringUtils.splitByCharacterTypeCamelCase("ab:cd:ef")));

        assertTrue(Objects.deepEquals(new String[]{"number", "5"},
                StringUtils.splitByCharacterTypeCamelCase("number5")));

        assertTrue(Objects.deepEquals(new String[]{"foo", "Bar"},
                StringUtils.splitByCharacterTypeCamelCase("fooBar")));

        assertTrue(Objects.deepEquals(new String[]{"foo", "200", "Bar"},
                StringUtils.splitByCharacterTypeCamelCase("foo200Bar")));

        assertTrue(Objects.deepEquals(new String[]{"ASF", "Rules"},
                StringUtils.splitByCharacterTypeCamelCase("ASFRules")));

        // A supplementary upper-case letter immediately before a lower-case run joins the following token,
        // exactly as a BMP upper-case letter does. U+1D400 MATHEMATICAL BOLD CAPITAL A is an upper-case letter.
        final String boldA = new String(Character.toChars(0x1D400));
        assertTrue(Objects.deepEquals(new String[]{boldA + "bc"},
                StringUtils.splitByCharacterTypeCamelCase(boldA + "bc")));
        assertTrue(Objects.deepEquals(new String[]{"AB", boldA + "cd"},
                StringUtils.splitByCharacterTypeCamelCase("AB" + boldA + "cd")));
        assertTrue(Objects.deepEquals(new String[]{"foo", boldA + "bar"},
                StringUtils.splitByCharacterTypeCamelCase("foo" + boldA + "bar")));
    }

    @Test
    void testSplitByWholeSeparatorPreserveAllTokens_StringString() {
        assertArrayEquals(null, StringUtils.splitByWholeSeparatorPreserveAllTokens(null, "."));

        assertEquals(0, StringUtils.splitByWholeSeparatorPreserveAllTokens("", ".").length);

        // test whitespace
        String input = "ab   de fg";
        String[] expected = {"ab", "", "", "de", "fg"};

        String[] actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, null);
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }

        // test delimiter singlechar
        input = "1::2:::3::::4";
        expected = new String[]{"1", "", "2", "", "", "3", "", "", "", "4"};

        actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, ":");
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }

        // test delimiter multichar
        input = "1::2:::3::::4";
        expected = new String[]{"1", "2", ":3", "", "4"};

        actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, "::");
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }
    }

    @Test
    void testSplitByWholeSeparatorPreserveAllTokens_StringStringInt() {
        assertArrayEquals(null, StringUtils.splitByWholeSeparatorPreserveAllTokens(null, ".", -1));

        assertEquals(0, StringUtils.splitByWholeSeparatorPreserveAllTokens("", ".", -1).length);

        // test whitespace
        String input = "ab   de fg";
        String[] expected = {"ab", "", "", "de", "fg"};

        String[] actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, null, -1);
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }

        // test delimiter singlechar
        input = "1::2:::3::::4";
        expected = new String[]{"1", "", "2", "", "", "3", "", "", "", "4"};

        actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, ":", -1);
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }

        // test delimiter multichar
        input = "1::2:::3::::4";
        expected = new String[]{"1", "2", ":3", "", "4"};

        actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, "::", -1);
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }

        // test delimiter char with max
        input = "1::2::3:4";
        expected = new String[]{"1", "", "2", ":3:4"};

        actual = StringUtils.splitByWholeSeparatorPreserveAllTokens(input, ":", 4);
        assertEquals(expected.length, actual.length);
        for (int i = 0; i < actual.length; i += 1) {
            assertEquals(expected[i], actual[i]);
        }
    }

    @Test
    void testSplitByWholeString_StringStringBoolean() {
        assertArrayEquals(null, StringUtils.splitByWholeSeparator(null, "."));

        assertEquals(0, StringUtils.splitByWholeSeparator("", ".").length);

        final String stringToSplitOnNulls = "ab   de fg";
        final String[] splitOnNullExpectedResults = {"ab", "de", "fg"};

        final String[] splitOnNullResults = StringUtils.splitByWholeSeparator(stringToSplitOnNulls, null);
        assertEquals(splitOnNullExpectedResults.length, splitOnNullResults.length);
        for (int i = 0; i < splitOnNullExpectedResults.length; i += 1) {
            assertEquals(splitOnNullExpectedResults[i], splitOnNullResults[i]);
        }

        final String stringToSplitOnCharactersAndString = "abstemiouslyaeiouyabstemiously";

        final String[] splitOnStringExpectedResults = {"abstemiously", "abstemiously"};
        final String[] splitOnStringResults = StringUtils.splitByWholeSeparator(stringToSplitOnCharactersAndString, "aeiouy");
        assertEquals(splitOnStringExpectedResults.length, splitOnStringResults.length);
        for (int i = 0; i < splitOnStringExpectedResults.length; i += 1) {
            assertEquals(splitOnStringExpectedResults[i], splitOnStringResults[i]);
        }

        final String[] splitWithMultipleSeparatorExpectedResults = {"ab", "cd", "ef"};
        final String[] splitWithMultipleSeparator = StringUtils.splitByWholeSeparator("ab:cd::ef", ":");
        assertEquals(splitWithMultipleSeparatorExpectedResults.length, splitWithMultipleSeparator.length);
        for (int i = 0; i < splitWithMultipleSeparatorExpectedResults.length; i++) {
            assertEquals(splitWithMultipleSeparatorExpectedResults[i], splitWithMultipleSeparator[i]);
        }
    }

    @Test
    void testSplitByWholeString_StringStringBooleanInt() {
        assertArrayEquals(null, StringUtils.splitByWholeSeparator(null, ".", 3));

        assertEquals(0, StringUtils.splitByWholeSeparator("", ".", 3).length);

        final String stringToSplitOnNulls = "ab   de fg";
        final String[] splitOnNullExpectedResults = {"ab", "de fg"};
        //String[] splitOnNullExpectedResults = { "ab", "de" } ;

        final String[] splitOnNullResults = StringUtils.splitByWholeSeparator(stringToSplitOnNulls, null, 2);
        assertEquals(splitOnNullExpectedResults.length, splitOnNullResults.length);
        for (int i = 0; i < splitOnNullExpectedResults.length; i += 1) {
            assertEquals(splitOnNullExpectedResults[i], splitOnNullResults[i]);
        }

        final String stringToSplitOnCharactersAndString = "abstemiouslyaeiouyabstemiouslyaeiouyabstemiously";

        final String[] splitOnStringExpectedResults = {"abstemiously", "abstemiouslyaeiouyabstemiously"};
        //String[] splitOnStringExpectedResults = { "abstemiously", "abstemiously" } ;
        final String[] splitOnStringResults = StringUtils.splitByWholeSeparator(stringToSplitOnCharactersAndString, "aeiouy", 2);
        assertEquals(splitOnStringExpectedResults.length, splitOnStringResults.length);
        for (int i = 0; i < splitOnStringExpectedResults.length; i++) {
            assertEquals(splitOnStringExpectedResults[i], splitOnStringResults[i]);
        }
    }

    @ParameterizedTest
    @CsvSource({
        "a:b:,       :,   'a,b'",
        "a:,         :,   a",
        "ab-!-cd-!-, -!-, 'ab,cd'",
    })
    void testSplitByWholeStringDropsTrailingEmpty(final String str, final String separator, final String expected) {
        final String[] expectedTokens = expected.split(",");
        // a trailing separator must not leak an empty token (it is dropped, like leading and adjacent ones)
        assertArrayEquals(expectedTokens, StringUtils.splitByWholeSeparator(str, separator));
        // the preserve-all-tokens variant still keeps the trailing empty token
        assertArrayEquals(ArrayUtils.add(expectedTokens, ""), StringUtils.splitByWholeSeparatorPreserveAllTokens(str, separator));
    }

    @Test
    void testSplitPreserveAllTokens_String() {
        assertNull(StringUtils.splitPreserveAllTokens(null));
        assertEquals(0, StringUtils.splitPreserveAllTokens("").length);

        String str = "abc def";
        String[] res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(2, res.length);
        assertEquals("abc", res[0]);
        assertEquals("def", res[1]);

        str = "abc  def";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(3, res.length);
        assertEquals("abc", res[0]);
        assertEquals("", res[1]);
        assertEquals("def", res[2]);

        str = " abc ";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(3, res.length);
        assertEquals("", res[0]);
        assertEquals("abc", res[1]);
        assertEquals("", res[2]);

        str = "a b .c";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(3, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals(".c", res[2]);

        str = " a b .c";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(4, res.length);
        assertEquals("", res[0]);
        assertEquals("a", res[1]);
        assertEquals("b", res[2]);
        assertEquals(".c", res[3]);

        str = "a  b  .c";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(5, res.length);
        assertEquals("a", res[0]);
        assertEquals("", res[1]);
        assertEquals("b", res[2]);
        assertEquals("", res[3]);
        assertEquals(".c", res[4]);

        str = " a  ";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(4, res.length);
        assertEquals("", res[0]);
        assertEquals("a", res[1]);
        assertEquals("", res[2]);
        assertEquals("", res[3]);

        str = " a  b";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(4, res.length);
        assertEquals("", res[0]);
        assertEquals("a", res[1]);
        assertEquals("", res[2]);
        assertEquals("b", res[3]);

        str = "a" + WHITESPACE + "b" + NON_WHITESPACE + "c";
        res = StringUtils.splitPreserveAllTokens(str);
        assertEquals(WHITESPACE.length() + 1, res.length);
        assertEquals("a", res[0]);
        for (int i = 1; i < WHITESPACE.length() - 1; i++) {
            assertEquals("", res[i]);
        }
        assertEquals("b" + NON_WHITESPACE + "c", res[WHITESPACE.length()]);
    }

    @Test
    void testSplitPreserveAllTokens_StringChar() {
        assertNull(StringUtils.splitPreserveAllTokens(null, '.'));
        assertEquals(0, StringUtils.splitPreserveAllTokens("", '.').length);

        String str = "a.b. c";
        String[] res = StringUtils.splitPreserveAllTokens(str, '.');
        assertEquals(3, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals(" c", res[2]);

        str = "a.b.. c";
        res = StringUtils.splitPreserveAllTokens(str, '.');
        assertEquals(4, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals("", res[2]);
        assertEquals(" c", res[3]);

        str = ".a.";
        res = StringUtils.splitPreserveAllTokens(str, '.');
        assertEquals(3, res.length);
        assertEquals("", res[0]);
        assertEquals("a", res[1]);
        assertEquals("", res[2]);

        str = ".a..";
        res = StringUtils.splitPreserveAllTokens(str, '.');
        assertEquals(4, res.length);
        assertEquals("", res[0]);
        assertEquals("a", res[1]);
        assertEquals("", res[2]);
        assertEquals("", res[3]);

        str = "..a.";
        res = StringUtils.splitPreserveAllTokens(str, '.');
        assertEquals(4, res.length);
        assertEquals("", res[0]);
        assertEquals("", res[1]);
        assertEquals("a", res[2]);
        assertEquals("", res[3]);

        str = "..a";
        res = StringUtils.splitPreserveAllTokens(str, '.');
        assertEquals(3, res.length);
        assertEquals("", res[0]);
        assertEquals("", res[1]);
        assertEquals("a", res[2]);

        str = "a b c";
        res = StringUtils.splitPreserveAllTokens(str, ' ');
        assertEquals(3, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals("c", res[2]);

        str = "a  b  c";
        res = StringUtils.splitPreserveAllTokens(str, ' ');
        assertEquals(5, res.length);
        assertEquals("a", res[0]);
        assertEquals("", res[1]);
        assertEquals("b", res[2]);
        assertEquals("", res[3]);
        assertEquals("c", res[4]);

        str = " a b c";
        res = StringUtils.splitPreserveAllTokens(str, ' ');
        assertEquals(4, res.length);
        assertEquals("", res[0]);
        assertEquals("a", res[1]);
        assertEquals("b", res[2]);
        assertEquals("c", res[3]);

        str = "  a b c";
        res = StringUtils.splitPreserveAllTokens(str, ' ');
        assertEquals(5, res.length);
        assertEquals("", res[0]);
        assertEquals("", res[1]);
        assertEquals("a", res[2]);
        assertEquals("b", res[3]);
        assertEquals("c", res[4]);

        str = "a b c ";
        res = StringUtils.splitPreserveAllTokens(str, ' ');
        assertEquals(4, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals("c", res[2]);
        assertEquals("", res[3]);

        str = "a b c  ";
        res = StringUtils.splitPreserveAllTokens(str, ' ');
        assertEquals(5, res.length);
        assertEquals("a", res[0]);
        assertEquals("b", res[1]);
        assertEquals("c", res[2]);
        assertEquals("", res[3]);
        assertEquals("", res[4]);

        // Match example in javadoc
        {
            final String[] results;
            final String[] expectedResults = {"a", "", "b", "c"};
            results = StringUtils.splitPreserveAllTokens("a..b.c", '.');
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }
    }

    @Test
    void testSplitPreserveAllTokens_StringString_StringStringInt() {
        assertNull(StringUtils.splitPreserveAllTokens(null, "."));
        assertNull(StringUtils.splitPreserveAllTokens(null, ".", 3));

        assertEquals(0, StringUtils.splitPreserveAllTokens("", ".").length);
        assertEquals(0, StringUtils.splitPreserveAllTokens("", ".", 3).length);

        innerTestSplitPreserveAllTokens('.', ".", ' ');
        innerTestSplitPreserveAllTokens('.', ".", ',');
        innerTestSplitPreserveAllTokens('.', ".,", 'x');
        for (int i = 0; i < WHITESPACE.length(); i++) {
            for (int j = 0; j < NON_WHITESPACE.length(); j++) {
                innerTestSplitPreserveAllTokens(WHITESPACE.charAt(i), null, NON_WHITESPACE.charAt(j));
                innerTestSplitPreserveAllTokens(WHITESPACE.charAt(i), String.valueOf(WHITESPACE.charAt(i)), NON_WHITESPACE.charAt(j));
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "de fg"};
            results = StringUtils.splitPreserveAllTokens("ab de fg", null, 2);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "  de fg"};
            results = StringUtils.splitPreserveAllTokens("ab   de fg", null, 2);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "::de:fg"};
            results = StringUtils.splitPreserveAllTokens("ab:::de:fg", ":", 2);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "", " de fg"};
            results = StringUtils.splitPreserveAllTokens("ab   de fg", null, 3);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "", "", "de fg"};
            results = StringUtils.splitPreserveAllTokens("ab   de fg", null, 4);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] expectedResults = {"ab", "cd:ef"};
            final String[] results;
            results = StringUtils.splitPreserveAllTokens("ab:cd:ef", ":", 2);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", ":cd:ef"};
            results = StringUtils.splitPreserveAllTokens("ab::cd:ef", ":", 2);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "", ":cd:ef"};
            results = StringUtils.splitPreserveAllTokens("ab:::cd:ef", ":", 3);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"ab", "", "", "cd:ef"};
            results = StringUtils.splitPreserveAllTokens("ab:::cd:ef", ":", 4);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"", "ab", "", "", "cd:ef"};
            results = StringUtils.splitPreserveAllTokens(":ab:::cd:ef", ":", 5);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

        {
            final String[] results;
            final String[] expectedResults = {"", "", "ab", "", "", "cd:ef"};
            results = StringUtils.splitPreserveAllTokens("::ab:::cd:ef", ":", 6);
            assertEquals(expectedResults.length, results.length);
            for (int i = 0; i < expectedResults.length; i++) {
                assertEquals(expectedResults[i], results[i]);
            }
        }

    }

    // Methods on StringUtils that are immutable in spirit (i.e. calculate the length)
    // should take a CharSequence parameter. Methods that are mutable in spirit (i.e. capitalize)
    // should take a String or String[] parameter and return String or String[].
    // This test enforces that this is done.
    @Test
    void testStringUtilsCharSequenceContract() {
        final Class<StringUtils> c = StringUtils.class;
        // Methods that are expressly excluded from testStringUtilsCharSequenceContract()
        final String[] excludeMethods = {
            "public static int org.apache.commons.lang3.StringUtils.compare(java.lang.String,java.lang.String)",
            "public static int org.apache.commons.lang3.StringUtils.compare(java.lang.String,java.lang.String,boolean)",
            "public static int org.apache.commons.lang3.StringUtils.compareIgnoreCase(java.lang.String,java.lang.String)",
            "public static int org.apache.commons.lang3.StringUtils.compareIgnoreCase(java.lang.String,java.lang.String,boolean)",
            "public static byte[] org.apache.commons.lang3.StringUtils.getBytes(java.lang.String,java.nio.charset.Charset)",
            "public static byte[] org.apache.commons.lang3.StringUtils.getBytes(java.lang.String,java.lang.String) throws java.io.UnsupportedEncodingException"
        };
        final Method[] methods = c.getMethods();

        for (final Method m : methods) {
            final String methodStr = m.toString();
            if (m.getReturnType() == String.class || m.getReturnType() == String[].class) {
                // Assume this is mutable and ensure the first parameter is not CharSequence.
                // It may be String or it may be something else (String[], Object, Object[]) so
                // don't actively test for that.
                final Class<?>[] params = m.getParameterTypes();
                if (params.length > 0 && (params[0] == CharSequence.class || params[0] == CharSequence[].class)) {
                    assertFalse(ArrayUtils.contains(excludeMethods, methodStr), "The method \"" + methodStr + "\" appears to be mutable in spirit and therefore must not accept a CharSequence");
                }
            } else {
                // Assume this is immutable in spirit and ensure the first parameter is not String.
                // As above, it may be something other than CharSequence.
                final Class<?>[] params = m.getParameterTypes();
                if (params.length > 0 && (params[0] == String.class || params[0] == String[].class)) {
                    assertTrue(ArrayUtils.contains(excludeMethods, methodStr),
                            "The method \"" + methodStr + "\" appears to be immutable in spirit and therefore must not accept a String");
                }
            }
        }
    }

    @Test
    void testSwapCase_String() {
        assertNull(StringUtils.swapCase(null));
        assertEquals("", StringUtils.swapCase(""));
        assertEquals("  ", StringUtils.swapCase("  "));

        assertEquals("i", WordUtils.swapCase("I"));
        assertEquals("I", WordUtils.swapCase("i"));
        assertEquals("I AM HERE 123", StringUtils.swapCase("i am here 123"));
        assertEquals("i aM hERE 123", StringUtils.swapCase("I Am Here 123"));
        assertEquals("I AM here 123", StringUtils.swapCase("i am HERE 123"));
        assertEquals("i am here 123", StringUtils.swapCase("I AM HERE 123"));

        final String test = "This String contains a TitleCase character: \u01C8";
        final String expect = "tHIS sTRING CONTAINS A tITLEcASE CHARACTER: \u01C9";
        assertEquals(expect, WordUtils.swapCase(test));
        assertEquals(expect, StringUtils.swapCase(test));
    }

    @Test
    void testToCodePoints() {
        final int orphanedHighSurrogate = 0xD801;
        final int orphanedLowSurrogate = 0xDC00;
        final int supplementary = 0x2070E;
        final int[] codePoints = { 'a', orphanedHighSurrogate, 'b', 'c', supplementary, 'd', orphanedLowSurrogate, 'e' };
        final String s = new String(codePoints, 0, codePoints.length);
        assertArrayEquals(codePoints, StringUtils.toCodePoints(s));
        assertNull(StringUtils.toCodePoints(null));
        assertArrayEquals(ArrayUtils.EMPTY_INT_ARRAY, StringUtils.toCodePoints(""));
        assertArrayEquals(new int[] { 'a' }, StringUtils.toCodePoints("a"));
        assertArrayEquals(new int[] { 'a', 'b' }, StringUtils.toCodePoints("ab"));
        assertArrayEquals(new int[] { 'a', 'b', 'c' }, StringUtils.toCodePoints("abc"));
    }

    @Test
    void testToCodePointsEmoji() {
        assertArrayEquals(ArrayFill.fill(new int[14], 129418), StringUtils.toCodePoints("🦊🦊🦊🦊🦊🦊🦊🦊🦊🦊🦊🦊🦊🦊"));
        assertArrayEquals(new int[] { 128105, 127995, 8205, 128104, 127995, 8205, 128102, 127995, 8205, 128102, 127995, 128105, 127996, 8205, 128104, 127996,
                8205, 128102, 127996, 8205, 128102, 127996, 128105, 127997, 8205, 128104, 127997, 8205, 128102, 127997, 8205, 128102, 127997, 128105, 127998,
                8205, 128104, 127998, 8205, 128102, 127998, 8205, 128102, 127998, 128105, 127999, 8205, 128104, 127999, 8205, 128102, 127999, 8205, 128102,
                127999, 128105, 127995, 8205, 128104, 127995, 8205, 128102, 127995, 8205, 128102, 127995, 128105, 127996, 8205, 128104, 127996, 8205, 128102,
                127996, 8205, 128102, 127996, 128105, 127997, 8205, 128104, 127997, 8205, 128102, 127997, 8205, 128102, 127997, 128105, 127998, 8205, 128104,
                127998, 8205, 128102, 127998, 8205, 128102, 127998, 128105, 127999, 8205, 128104, 127999, 8205, 128102, 127999, 8205, 128102, 127999 },
                StringUtils.toCodePoints(
                        "👩🏻‍👨🏻‍👦🏻‍👦🏻👩🏼‍👨🏼‍👦🏼‍👦🏼👩🏽‍👨🏽‍👦🏽‍👦🏽👩🏾‍👨🏾‍👦🏾‍👦🏾👩🏿‍👨🏿‍👦🏿‍👦🏿👩🏻‍👨🏻‍👦🏻‍👦🏻👩🏼‍👨🏼‍👦🏼‍👦🏼👩🏽‍👨🏽‍👦🏽‍👦🏽👩🏾‍👨🏾‍👦🏾‍👦🏾👩🏿‍👨🏿‍👦🏿‍👦🏿"));
    }

    /**
     * Tests {@link StringUtils#toEncodedString(byte[], Charset)}
     *
     * @see StringUtils#toEncodedString(byte[], Charset)
     */
    @Test
    void testToEncodedString() {
        final String expectedString = "The quick brown fox jumps over the lazy dog.";
        String encoding = SystemUtils.FILE_ENCODING;
        byte[] expectedBytes = expectedString.getBytes(Charset.defaultCharset());
        // sanity check start
        assertArrayEquals(expectedBytes, expectedString.getBytes());
        // sanity check end
        assertEquals(expectedString, StringUtils.toEncodedString(expectedBytes, Charset.defaultCharset()));
        assertEquals(expectedString, StringUtils.toEncodedString(expectedBytes, Charset.forName(encoding)));
        encoding = StandardCharsets.UTF_16.name();
        expectedBytes = expectedString.getBytes(Charset.forName(encoding));
        assertEquals(expectedString, StringUtils.toEncodedString(expectedBytes, Charset.forName(encoding)));
    }

    @Test
    @ReadsDefaultLocale
    @WritesDefaultLocale
    void testToRootLowerCase() {
        assertNull(StringUtils.toRootLowerCase(null));
        assertEquals("a", StringUtils.toRootLowerCase("A"));
        assertEquals("a", StringUtils.toRootLowerCase("a"));
        final Locale TURKISH = Locale.forLanguageTag("tr");
        // Sanity checks:
        assertNotEquals("title", "TITLE".toLowerCase(TURKISH));
        assertEquals("title", "TITLE".toLowerCase(Locale.ROOT));
        assertEquals("title", StringUtils.toRootLowerCase("TITLE"));
    }

    @Test
    @DefaultLocale("tr")
    @ReadsDefaultLocale
    void testToRootLowerCaseTurkish() {
        assertEquals("title", StringUtils.toRootLowerCase("TITLE"));
    }

    @Test
    @ReadsDefaultLocale
    @WritesDefaultLocale
    void testToRootUpperCase() {
        assertNull(StringUtils.toRootUpperCase(null));
        assertEquals("A", StringUtils.toRootUpperCase("a"));
        assertEquals("A", StringUtils.toRootUpperCase("A"));
        final Locale TURKISH = Locale.forLanguageTag("tr");
        // Sanity checks:
        assertNotEquals("TITLE", "title".toUpperCase(TURKISH));
        assertEquals("TITLE", "title".toUpperCase(Locale.ROOT));
        assertEquals("TITLE", StringUtils.toRootUpperCase("title"));
        // Make sure we are not using the default Locale:
        final Locale defaultLocale = Locale.getDefault();
        try {
            Locale.setDefault(TURKISH);
            assertEquals("TITLE", StringUtils.toRootUpperCase("title"));
        } finally {
            Locale.setDefault(defaultLocale);
        }
    }

    /**
     * Tests {@link StringUtils#toString(byte[], String)}
     *
     * @throws UnsupportedEncodingException because the method under test max throw it
     * @see StringUtils#toString(byte[], String)
     */
    @Test
    void testToString() throws UnsupportedEncodingException {
        final String expectedString = "The quick brown fox jumps over the lazy dog.";
        byte[] expectedBytes = expectedString.getBytes(Charset.defaultCharset());
        // sanity check start
        assertArrayEquals(expectedBytes, expectedString.getBytes());
        // sanity check end
        assertEquals(expectedString, StringUtils.toString(expectedBytes, null));
        assertEquals(expectedString, StringUtils.toString(expectedBytes, SystemUtils.FILE_ENCODING));
        final String encoding = StandardCharsets.UTF_16.name();
        expectedBytes = expectedString.getBytes(Charset.forName(encoding));
        assertEquals(expectedString, StringUtils.toString(expectedBytes, encoding));
    }

    @Test
    void testTruncate_StringInt() {
        assertNull(StringUtils.truncate(null, 12));
        assertIllegalArgumentException(() -> StringUtils.truncate(null, -1), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate(null, -10), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate(null, Integer.MIN_VALUE), "maxWidth cannot be negative");
        assertEquals("", StringUtils.truncate("", 10));
        assertEquals("abc", StringUtils.truncate("abcdefghij", 3));
        assertEquals("abcdef", StringUtils.truncate("abcdefghij", 6));
        assertEquals("", StringUtils.truncate("abcdefghij", 0));
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -1), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -100), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", Integer.MIN_VALUE), "maxWidth cannot be negative");
        assertEquals("abcdefghij", StringUtils.truncate("abcdefghijklmno", 10));
        assertEquals("abcdefghijklmno", StringUtils.truncate("abcdefghijklmno", Integer.MAX_VALUE));
        assertEquals("abcde", StringUtils.truncate("abcdefghijklmno", 5));
        assertEquals("abc", StringUtils.truncate("abcdefghijklmno", 3));
    }

    @Test
    void testTruncate_StringIntInt() {
        assertNull(StringUtils.truncate(null, 0, 12));
        assertIllegalArgumentException(() -> StringUtils.truncate(null, -1, 0), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate(null, -10, -4), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate(null, Integer.MIN_VALUE, Integer.MIN_VALUE), "offset cannot be negative");
        assertNull(StringUtils.truncate(null, 10, 12));
        assertEquals("", StringUtils.truncate("", 0, 10));
        assertEquals("", StringUtils.truncate("", 2, 10));
        assertEquals("abc", StringUtils.truncate("abcdefghij", 0, 3));
        assertEquals("fghij", StringUtils.truncate("abcdefghij", 5, 6));
        assertEquals("", StringUtils.truncate("abcdefghij", 0, 0));
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", 0, -1), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", 0, -10), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", 0, -100), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", 1, -100), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", 0, Integer.MIN_VALUE), "maxWidth cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -1, 0), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -10, 0), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -100, 1), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", Integer.MIN_VALUE, 0), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -1, -1), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -10, -10), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", -100, -100), "offset cannot be negative");
        assertIllegalArgumentException(() -> StringUtils.truncate("abcdefghij", Integer.MIN_VALUE, Integer.MIN_VALUE),
                "offset cannot be negative");
        final String raspberry = "raspberry peach";
        assertEquals("peach", StringUtils.truncate(raspberry, 10, 15));
        assertEquals("abcdefghij", StringUtils.truncate("abcdefghijklmno", 0, 10));
        assertEquals("abcdefghijklmno", StringUtils.truncate("abcdefghijklmno", 0, Integer.MAX_VALUE));
        assertEquals("bcdefghijk", StringUtils.truncate("abcdefghijklmno", 1, 10));
        assertEquals("cdefghijkl", StringUtils.truncate("abcdefghijklmno", 2, 10));
        assertEquals("defghijklm", StringUtils.truncate("abcdefghijklmno", 3, 10));
        assertEquals("efghijklmn", StringUtils.truncate("abcdefghijklmno", 4, 10));
        assertEquals("fghijklmno", StringUtils.truncate("abcdefghijklmno", 5, 10));
        assertEquals("fghij", StringUtils.truncate("abcdefghijklmno", 5, 5));
        assertEquals("fgh", StringUtils.truncate("abcdefghijklmno", 5, 3));
        assertEquals("klm", StringUtils.truncate("abcdefghijklmno", 10, 3));
        assertEquals("klmno", StringUtils.truncate("abcdefghijklmno", 10, Integer.MAX_VALUE));
        assertEquals("n", StringUtils.truncate("abcdefghijklmno", 13, 1));
        assertEquals("no", StringUtils.truncate("abcdefghijklmno", 13, Integer.MAX_VALUE));
        assertEquals("o", StringUtils.truncate("abcdefghijklmno", 14, 1));
        assertEquals("o", StringUtils.truncate("abcdefghijklmno", 14, Integer.MAX_VALUE));
        assertEquals("", StringUtils.truncate("abcdefghijklmno", 15, 1));
        assertEquals("", StringUtils.truncate("abcdefghijklmno", 15, Integer.MAX_VALUE));
        assertEquals("", StringUtils.truncate("abcdefghijklmno", Integer.MAX_VALUE, Integer.MAX_VALUE));
    }

    @Test
    void testTruncate_StringIntInt_surrogatePair() {
        // U+1F600 GRINNING FACE is a single supplementary code point stored as a surrogate pair
        final String grin = "😀";
        // a cut that would land between the two halves keeps the result well formed instead of emitting a lone surrogate
        assertEquals("a", StringUtils.truncate("a" + grin + "b", 0, 2));
        assertEquals(grin, StringUtils.truncate("a" + grin + "b", 1, 2));
        assertEquals("ab", StringUtils.truncate("ab" + grin, 0, 3));
        // an offset that lands inside a pair skips the orphaned low surrogate
        assertEquals("a", StringUtils.truncate(grin + "ab", 1, 2));
        // an input that is only the pair stays whole or drops to empty, never a lone surrogate
        assertEquals(grin, StringUtils.truncate(grin, 0, 2));
        assertEquals(grin, StringUtils.truncate(grin, 0, 3));
        assertEquals("", StringUtils.truncate(grin, 0, 0));
        assertEquals("", StringUtils.truncate(grin, 0, 1));
        assertEquals("", StringUtils.truncate(grin, 1, 1));
        assertEquals("", StringUtils.truncate(grin, 1, 2));
        assertEquals("", StringUtils.truncate(grin, 2, 2));
    }

    @Test
    void testUnCapitalize() {
        assertNull(StringUtils.uncapitalize(null));

        assertEquals(FOO_UNCAP, StringUtils.uncapitalize(FOO_CAP), "uncapitalize(String) failed");
        assertEquals(FOO_UNCAP, StringUtils.uncapitalize(FOO_UNCAP), "uncapitalize(string) failed");
        assertEquals("", StringUtils.uncapitalize(""), "uncapitalize(empty-string) failed");
        assertEquals("x", StringUtils.uncapitalize("X"), "uncapitalize(single-char-string) failed");

        // Examples from uncapitalize Javadoc
        assertEquals("cat", StringUtils.uncapitalize("cat"));
        assertEquals("cat", StringUtils.uncapitalize("Cat"));
        assertEquals("cAT", StringUtils.uncapitalize("CAT"));
    }

    @Test
    void testUnescapeSurrogatePairs() {
        assertEquals("\uD83D\uDE30", StringEscapeUtils.unescapeCsv("\uD83D\uDE30"));
        // Examples from https://en.wikipedia.org/wiki/UTF-16
        assertEquals("\uD800\uDC00", StringEscapeUtils.unescapeCsv("\uD800\uDC00"));
        assertEquals("\uD834\uDD1E", StringEscapeUtils.unescapeCsv("\uD834\uDD1E"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.unescapeCsv("\uDBFF\uDFFD"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.unescapeHtml3("\uDBFF\uDFFD"));
        assertEquals("\uDBFF\uDFFD", StringEscapeUtils.unescapeHtml4("\uDBFF\uDFFD"));
    }

    @Test
    void testUnwrap_StringChar() {
        assertNull(StringUtils.unwrap(null, null));
        assertNull(StringUtils.unwrap(null, CharUtils.NUL));
        assertNull(StringUtils.unwrap(null, '1'));

        assertEquals("abc", StringUtils.unwrap("abc", null));
        assertEquals("a", StringUtils.unwrap("a", "a"));
        assertEquals("", StringUtils.unwrap("aa", "a"));
        assertEquals("abc", StringUtils.unwrap("\'abc\'", '\''));
        assertEquals("abc", StringUtils.unwrap("AabcA", 'A'));
        assertEquals("AabcA", StringUtils.unwrap("AAabcAA", 'A'));
        assertEquals("abc", StringUtils.unwrap("abc", 'b'));
        assertEquals("#A", StringUtils.unwrap("#A", '#'));
        assertEquals("A#", StringUtils.unwrap("A#", '#'));
        assertEquals("ABA", StringUtils.unwrap("AABAA", 'A'));
    }

    @Test
    void testUnwrap_StringString() {
        assertNull(StringUtils.unwrap(null, null));
        assertNull(StringUtils.unwrap(null, ""));
        assertNull(StringUtils.unwrap(null, "1"));

        assertEquals("abc", StringUtils.unwrap("abc", null));
        assertEquals("abc", StringUtils.unwrap("abc", ""));
        assertEquals("a", StringUtils.unwrap("a", "a"));
        assertEquals("ababa", StringUtils.unwrap("ababa", "aba"));
        assertEquals("", StringUtils.unwrap("aa", "a"));
        assertEquals("abc", StringUtils.unwrap("\'abc\'", "\'"));
        assertEquals("abc", StringUtils.unwrap("\"abc\"", "\""));
        assertEquals("abc\"xyz", StringUtils.unwrap("\"abc\"xyz\"", "\""));
        assertEquals("abc\"xyz\"", StringUtils.unwrap("\"abc\"xyz\"\"", "\""));
        assertEquals("abc\'xyz\'", StringUtils.unwrap("\"abc\'xyz\'\"", "\""));
        assertEquals("\"abc\'xyz\'\"", StringUtils.unwrap("AA\"abc\'xyz\'\"AA", "AA"));
        assertEquals("\"abc\'xyz\'\"", StringUtils.unwrap("123\"abc\'xyz\'\"123", "123"));
        assertEquals("AA\"abc\'xyz\'\"", StringUtils.unwrap("AA\"abc\'xyz\'\"", "AA"));
        assertEquals("AA\"abc\'xyz\'\"AA", StringUtils.unwrap("AAA\"abc\'xyz\'\"AAA", "A"));
        assertEquals("\"abc\'xyz\'\"AA", StringUtils.unwrap("\"abc\'xyz\'\"AA", "AA"));
    }

    @Test
    void testUpperCase() {
        assertNull(StringUtils.upperCase(null));
        assertNull(StringUtils.upperCase(null, Locale.ENGLISH));
        assertEquals("FOO TEST THING", StringUtils.upperCase("fOo test THING"), "upperCase(String) failed");
        assertEquals("", StringUtils.upperCase(""), "upperCase(empty-string) failed");
        assertEquals("FOO TEST THING", StringUtils.upperCase("fOo test THING", Locale.ENGLISH),
                "upperCase(String, Locale) failed");
        assertEquals("", StringUtils.upperCase("", Locale.ENGLISH),
                "upperCase(empty-string, Locale) failed");
    }

    @Test
    void testWrap_StringChar() {
        assertNull(StringUtils.wrap(null, CharUtils.NUL));
        assertNull(StringUtils.wrap(null, '1'));

        assertEquals("", StringUtils.wrap("", CharUtils.NUL));
        assertEquals("xabx", StringUtils.wrap("ab", 'x'));
        assertEquals("\"ab\"", StringUtils.wrap("ab", '\"'));
        assertEquals("\"\"ab\"\"", StringUtils.wrap("\"ab\"", '\"'));
        assertEquals("'ab'", StringUtils.wrap("ab", '\''));
        assertEquals("''abcd''", StringUtils.wrap("'abcd'", '\''));
        assertEquals("'\"abcd\"'", StringUtils.wrap("\"abcd\"", '\''));
        assertEquals("\"'abcd'\"", StringUtils.wrap("'abcd'", '\"'));
    }

    @Test
    void testWrap_StringString() {
        assertNull(StringUtils.wrap(null, null));
        assertNull(StringUtils.wrap(null, ""));
        assertNull(StringUtils.wrap(null, "1"));

        assertNull(StringUtils.wrap(null, null));
        assertEquals("", StringUtils.wrap("", ""));
        assertEquals("ab", StringUtils.wrap("ab", null));
        assertEquals("xabx", StringUtils.wrap("ab", "x"));
        assertEquals("\"ab\"", StringUtils.wrap("ab", "\""));
        assertEquals("\"\"ab\"\"", StringUtils.wrap("\"ab\"", "\""));
        assertEquals("'ab'", StringUtils.wrap("ab", "'"));
        assertEquals("''abcd''", StringUtils.wrap("'abcd'", "'"));
        assertEquals("'\"abcd\"'", StringUtils.wrap("\"abcd\"", "'"));
        assertEquals("\"'abcd'\"", StringUtils.wrap("'abcd'", "\""));
    }

    @Test
    void testWrapIfMissing_StringChar() {
        assertNull(StringUtils.wrapIfMissing(null, CharUtils.NUL));
        assertNull(StringUtils.wrapIfMissing(null, '1'));

        assertEquals("", StringUtils.wrapIfMissing("", CharUtils.NUL));
        assertEquals("xabx", StringUtils.wrapIfMissing("ab", 'x'));
        assertEquals("\"ab\"", StringUtils.wrapIfMissing("ab", '\"'));
        assertEquals("\"ab\"", StringUtils.wrapIfMissing("\"ab\"", '\"'));
        assertEquals("'ab'", StringUtils.wrapIfMissing("ab", '\''));
        assertEquals("'abcd'", StringUtils.wrapIfMissing("'abcd'", '\''));
        assertEquals("'\"abcd\"'", StringUtils.wrapIfMissing("\"abcd\"", '\''));
        assertEquals("\"'abcd'\"", StringUtils.wrapIfMissing("'abcd'", '\"'));
        assertEquals("/x/", StringUtils.wrapIfMissing("x", '/'));
        assertEquals("/x/y/z/", StringUtils.wrapIfMissing("x/y/z", '/'));
        assertEquals("/x/y/z/", StringUtils.wrapIfMissing("/x/y/z", '/'));
        assertEquals("/x/y/z/", StringUtils.wrapIfMissing("x/y/z/", '/'));

        assertSame("/", StringUtils.wrapIfMissing("/", '/'));
        assertSame("/x/", StringUtils.wrapIfMissing("/x/", '/'));
    }

    @Test
    void testWrapIfMissing_StringString() {
        assertNull(StringUtils.wrapIfMissing(null, "\0"));
        assertNull(StringUtils.wrapIfMissing(null, "1"));

        assertEquals("", StringUtils.wrapIfMissing("", "\0"));
        assertEquals("xabx", StringUtils.wrapIfMissing("ab", "x"));
        assertEquals("\"ab\"", StringUtils.wrapIfMissing("ab", "\""));
        assertEquals("\"ab\"", StringUtils.wrapIfMissing("\"ab\"", "\""));
        assertEquals("'ab'", StringUtils.wrapIfMissing("ab", "\'"));
        assertEquals("'abcd'", StringUtils.wrapIfMissing("'abcd'", "\'"));
        assertEquals("'\"abcd\"'", StringUtils.wrapIfMissing("\"abcd\"", "\'"));
        assertEquals("\"'abcd'\"", StringUtils.wrapIfMissing("'abcd'", "\""));
        assertEquals("/x/", StringUtils.wrapIfMissing("x", "/"));
        assertEquals("/x/y/z/", StringUtils.wrapIfMissing("x/y/z", "/"));
        assertEquals("/x/y/z/", StringUtils.wrapIfMissing("/x/y/z", "/"));
        assertEquals("/x/y/z/", StringUtils.wrapIfMissing("x/y/z/", "/"));
        assertEquals("/", StringUtils.wrapIfMissing("/", "/"));
        assertEquals("ab/ab", StringUtils.wrapIfMissing("/", "ab"));

        assertSame("ab/ab", StringUtils.wrapIfMissing("ab/ab", "ab"));
        assertSame("//x//", StringUtils.wrapIfMissing("//x//", "//"));
    }
}