Add validations for enum range selection

Ensure `from` and `to` are empty when the enum has no constants, and
validate `from` comes before `to` like `EnumSet.range`. Mark the `from`
and `to` attributes as EXPERIMENTAL.

Resolves junit-team#4185.

documentation/src/test/java/example/ParameterizedTestDemo.java

@@ -174,7 +174,7 @@ void testWithEnumSourceRegex(ChronoUnit unit) {
 
 	// tag::EnumSource_range_exclude_example[]
 	@ParameterizedTest
-	@EnumSource(mode = EXCLUDE, from = "HOURS", to = "DAYS", names = { "HALF_DAYS" })
+	@EnumSource(from = "HOURS", to = "DAYS", mode = EXCLUDE, names = { "HALF_DAYS" })
 	void testWithEnumSourceRangeExclude(ChronoUnit unit) {
 		assertTrue(EnumSet.of(ChronoUnit.HOURS, ChronoUnit.DAYS).contains(unit));
 		assertFalse(EnumSet.of(ChronoUnit.HALF_DAYS).contains(unit));

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumArgumentsProvider.java

@@ -45,10 +45,16 @@ private <E extends Enum<E>> Set<? extends E> getEnumConstants(ExtensionContext c
 		Class<E> enumClass = determineEnumClass(context, enumSource);
 		E[] constants = enumClass.getEnumConstants();
 		if (constants.length == 0) {
+			Preconditions.condition(enumSource.from().isEmpty() && enumSource.to().isEmpty(),
+				"No enum constant in " + enumClass.getSimpleName() + ", but 'from' or 'to' is not empty.");
 			return EnumSet.noneOf(enumClass);
 		}
 		E from = enumSource.from().isEmpty() ? constants[0] : Enum.valueOf(enumClass, enumSource.from());
 		E to = enumSource.to().isEmpty() ? constants[constants.length - 1] : Enum.valueOf(enumClass, enumSource.to());
+		Preconditions.condition(from.compareTo(to) <= 0,
+			() -> String.format(
+				"Invalid enum range: 'from' (%s) must come before 'to' (%s) in the natural order of enum constants.",
+				from, to));
 		return EnumSet.range(from, to);
 	}
 

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumSource.java

@@ -99,7 +99,10 @@
 	 * @see #names
 	 * @see #to
 	 * @see #mode
+	 *
+	 * @since 5.12
 	 */
+	@API(status = EXPERIMENTAL, since = "5.12")
 	String from() default "";
 
 	/**
@@ -112,12 +115,19 @@
 	 * @see #names
 	 * @see #from
 	 * @see #mode
+	 *
+	 * @since 5.12
 	 */
+	@API(status = EXPERIMENTAL, since = "5.12")
 	String to() default "";
 
 	/**
 	 * The enum constant selection mode.
 	 *
+	 * <p>The mode only applies to the {@link #names} attribute and does not change
+	 * the behavior of {@link #from} and {@link #to}, which always define a range
+	 * based on the natural order of the enum constants.
+	 *
 	 * <p>Defaults to {@link Mode#INCLUDE INCLUDE}.
 	 *
 	 * @see Mode#INCLUDE
@@ -126,6 +136,8 @@
 	 * @see Mode#MATCH_ANY
 	 * @see Mode#MATCH_NONE
 	 * @see #names
+	 * @see #from
+	 * @see #to
 	 */
 	Mode mode() default Mode.INCLUDE;
 

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/EnumArgumentsProviderTests.java

@@ -164,6 +164,20 @@ void invalidEndingRangeIsDetected() {
 		assertThat(exception).hasMessageContaining("No enum constant");
 	}
 
+	@Test
+	void invalidRangeOrderIsDetected() {
+		Exception exception = assertThrows(PreconditionViolationException.class,
+			() -> provideArguments(EnumWithFourConstants.class, "BAR", "FOO", Mode.INCLUDE).findAny());
+		assertThat(exception).hasMessageContaining("Invalid enum range");
+	}
+
+	@Test
+	void invalidRangeIsDetectedWhenEnumWithNoConstantIsProvided() {
+		Exception exception = assertThrows(PreconditionViolationException.class,
+			() -> provideArguments(EnumWithNoConstant.class, "BAR", "FOO", Mode.INCLUDE).findAny());
+		assertThat(exception).hasMessageContaining("No enum constant");
+	}
+
 	static class TestCase {
 		void methodWithCorrectParameter(EnumWithFourConstants parameter) {
 		}