[refactor] extract picking a random enum value to method RandomService.nextEnum() (#1530)

* [refactor] extract picking a random enum value to method RandomService.nextEnum()

* add test for new method RandomService.nextEnum()

* reuse the new method `RandomService.nextEnum()` in `Options.option()`

the name "option" was not clearly indicating that it works with Enum.

Author: asolntsev

src/main/java/net/datafaker/providers/base/Finance.java

@@ -148,7 +148,7 @@ public String usRoutingNumber() {
     }
 
     private CreditCardType randomCreditCardType() {
-        return CreditCardType.values()[this.faker.random().nextInt(CreditCardType.values().length)];
+        return faker.random().nextEnum(CreditCardType.class);
     }
 
     private static String calculateIbanChecksum(String countryCode, String basicBankAccountNumber) {

src/main/java/net/datafaker/providers/base/Options.java

@@ -144,8 +144,7 @@ public final Set<String> subset(int size, String... options) {
      * @return A randomly selected element from the enum.
      */
     public <E extends Enum<E>> E option(Class<E> enumeration) {
-        E[] enumConstants = enumeration.getEnumConstants();
-        return enumConstants[faker.random().nextInt(enumConstants.length)];
+        return faker.random().nextEnum(enumeration);
     }
 
     /**

src/main/java/net/datafaker/service/RandomService.java

@@ -116,6 +116,11 @@ public byte[] nextRandomBytes(int numberOfBytes) {
         return randomBytes;
     }
 
+    public <T extends Enum<T>> T nextEnum(Class<T> klass) {
+        T[] enumConstants = klass.getEnumConstants();
+        return enumConstants[nextInt(enumConstants.length)];
+    }
+
     public String hex() {
         return hex(8);
     }

src/test/java/net/datafaker/service/RandomServiceTest.java

@@ -6,11 +6,19 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.CsvSource;
 import org.junit.jupiter.params.provider.MethodSource;
 
+import java.util.EnumSet;
+import java.util.List;
 import java.util.Random;
+import java.util.Set;
 import java.util.stream.Stream;
 
+import static net.datafaker.service.RandomServiceTest.Ring.DWARVES;
+import static net.datafaker.service.RandomServiceTest.Ring.ELVES;
+import static net.datafaker.service.RandomServiceTest.Ring.MEN;
+import static net.datafaker.service.RandomServiceTest.Ring.LORD;
 import static org.assertj.core.api.Assertions.allOf;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
@@ -145,6 +153,36 @@ void testDefaultHex(RandomService randomService) {
         assertThat(randomService.hex()).matches("^[0-9A-F]{8}$");
     }
 
+    @Test
+    void nextEnum() {
+        RandomService randomService = new RandomService();
+        Set<Ring> all = EnumSet.noneOf(Ring.class);
+        for (int i = 1; i < 200; i++) {
+            Ring actual = randomService.nextEnum(Ring.class);
+            all.add(actual);
+            assertThat(actual).isIn(ELVES, DWARVES, MEN, LORD);
+        }
+        assertThat(all).containsExactly(Ring.values());
+    }
+
+    @ParameterizedTest
+    @CsvSource({
+        "12345, DWARVES, MEN, LORD, LORD, LORD",
+        "42, MEN, ELVES, MEN, ELVES, DWARVES",
+    })
+    void predictableEnum(int seed, Ring expected1, Ring expected2, Ring expected3, Ring expected4, Ring expected5) {
+        RandomService randomService = new RandomService(new Random(seed));
+        assertThat(List.of(
+            randomService.nextEnum(Ring.class),
+            randomService.nextEnum(Ring.class),
+            randomService.nextEnum(Ring.class),
+            randomService.nextEnum(Ring.class),
+            randomService.nextEnum(Ring.class)
+        )).containsExactly(expected1, expected2, expected3, expected4, expected5);
+    }
+
+    enum Ring {ELVES, DWARVES, MEN, LORD}
+
     private static Stream<Arguments> randomServiceProvider() {
         return Stream.of(
             Arguments.of(new RandomService(), new RandomService(new Random()))