Add unit tests for ArrayUtils, Preconditions, ExtendedSafeRunner and StringConstants

This commit improves code coverage for utility classes in the
org.moreunit.core bundle.

Changes:
- Added ArrayUtilsTest.java
- Added PreconditionsTest.java (covering all methods and exception cases)
- Added ExtendedSafeRunnerTest.java (including exception handling)
- Added StringConstantsTest.java
- Improved StringsTest.java with coverage for emptyArray()
- Improved StringLengthComparatorTest.java with more precise assertions

These tests ensure that core utilities are robust and well-verified.

Co-authored-by: RoiSoleil <3462260+RoiSoleil@users.noreply.github.com>

Author: google-labs-jules[bot]

org.moreunit.core.test/test/org/moreunit/core/util/StringConstantsTest.java

@@ -0,0 +1,18 @@
+package org.moreunit.core.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class StringConstantsTest
+{
+    @Test
+    public void constants_should_have_expected_values()
+    {
+        assertThat(StringConstants.DOT).isEqualTo(".");
+        assertThat(StringConstants.EMPTY_STRING).isEqualTo("");
+        assertThat(StringConstants.NEWLINE).isEqualTo(System.getProperty("line.separator"));
+        assertThat(StringConstants.SLASH).isEqualTo("/");
+        assertThat(StringConstants.WILDCARD).isEqualTo("*");
+    }
+}

org.moreunit.core.test/test/org/moreunit/core/util/StringLengthComparatorTest.java

@@ -15,7 +15,7 @@ public void should_return_positive_integer_when_first_has_greater_length_than_se
     @Test
     public void should_return_negative_integer_when_second_has_greater_length_than_first_parameter() throws Exception
     {
-        assertThat(new StringLengthComparator().compare("", "Long")).isLessThanOrEqualTo(0);
+        assertThat(new StringLengthComparator().compare("", "Long")).isLessThan(0);
     }
 
     @Test