Remove built-in support for Locale conversion in ISO 639 format

documentation/src/docs/asciidoc/release-notes/release-notes-6.0.0-M2.adoc

@@ -26,6 +26,9 @@ repository on GitHub.
 * Deprecate `Launcher.execute(TestPlan, TestExecutionListener[])` and
   `Launcher.execute(LauncherDiscoveryRequest, TestExecutionListener[])` in favor of
   `Launcher.execute(LauncherExecutionRequest)`
+* `ConversionSupport` now converts `String` to `Locale` using the IETF BCP 47 language tag
+  format supported by the `Locale.forLanguageTag(String)` factory method instead of the
+  format used by the deprecated `Locale(String)` constructor.
 
 [[release-notes-6.0.0-M2-junit-platform-new-features-and-improvements]]
 ==== New Features and Improvements
@@ -65,6 +68,10 @@ repository on GitHub.
   of the `TestTemplateInvocationContextProvider` interface from
   `Stream<TestTemplateInvocationContext>` to
   `Stream<? extends TestTemplateInvocationContext>`.
+* Remove support for `junit.jupiter.params.arguments.conversion.locale.format`
+  configuration parameter. `Locale` conversions are now always performed using the IETF
+  BCP 47 language tag format supported by the `Locale.forLanguageTag(String)` factory
+  method.
 
 [[release-notes-6.0.0-M2-junit-jupiter-new-features-and-improvements]]
 ==== New Features and Improvements

documentation/src/docs/asciidoc/user-guide/writing-tests.adoc

@@ -2500,12 +2500,6 @@ integral types: `byte`, `short`, `int`, `long`, and their boxed counterparts.
 | `java.util.UUID`           | `"d043e930-7b3b-48e3-bdbe-5a3ccfb833db"` -> `UUID.fromString("d043e930-7b3b-48e3-bdbe-5a3ccfb833db")`
 |===
 
-WARNING: To revert to the old `java.util.Locale` conversion behavior of version 5.12 and
-earlier (which called the deprecated `Locale(String)` constructor), you can set the
-`junit.jupiter.params.arguments.conversion.locale.format`
-<<running-tests-config-params, configuration parameter>> to `iso_639`. However, please
-note that this parameter is deprecated and will be removed in a future release.
-
 [[writing-tests-parameterized-tests-argument-conversion-implicit-fallback]]
 ====== Fallback String-to-Object Conversion
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java

@@ -48,7 +48,10 @@
 @API(status = INTERNAL, since = "5.4")
 public class DefaultJupiterConfiguration implements JupiterConfiguration {
 
-	private static final List<String> UNSUPPORTED_CONFIGURATION_PARAMETERS = List.of("junit.jupiter.tempdir.scope");
+	private static final List<String> UNSUPPORTED_CONFIGURATION_PARAMETERS = List.of( //
+		"junit.jupiter.tempdir.scope", //
+		"junit.jupiter.params.arguments.conversion.locale.format" //
+	);
 
 	private static final EnumConfigurationParameterConverter<ExecutionMode> executionModeConverter = //
 		new EnumConfigurationParameterConverter<>(ExecutionMode.class, "parallel execution mode");
@@ -88,9 +91,9 @@ public DefaultJupiterConfiguration(ConfigurationParameters configurationParamete
 	private void validateConfigurationParameters(DiscoveryIssueReporter issueReporter) {
 		UNSUPPORTED_CONFIGURATION_PARAMETERS.forEach(key -> configurationParameters.get(key) //
 				.ifPresent(value -> {
-					var warning = DiscoveryIssue.create(Severity.WARNING,
-						"The '%s' configuration parameter is no longer supported: %s. Please remove it from your configuration.".formatted(
-							key, value));
+					var warning = DiscoveryIssue.create(Severity.WARNING, """
+							The '%s' configuration parameter is no longer supported. \
+							Please remove it from your configuration.""".formatted(key));
 					issueReporter.reportIssue(warning);
 				}));
 	}

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContext.java

@@ -74,7 +74,7 @@ private void storeParameterInfo(ExtensionContext context) {
 		ClassLoader classLoader = getClassLoader(this.declarationContext.getTestClass());
 		@Nullable
 		Object[] arguments = this.arguments.getConsumedPayloads();
-		ArgumentsAccessor accessor = DefaultArgumentsAccessor.create(context, invocationIndex, classLoader, arguments);
+		ArgumentsAccessor accessor = DefaultArgumentsAccessor.create(invocationIndex, classLoader, arguments);
 		new DefaultParameterInfo(declarations, accessor).store(context);
 	}
 

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolverFacade.java

@@ -435,7 +435,7 @@ private static Converter createConverter(ParameterDeclaration declaration, Exten
 					.map(clazz -> ParameterizedTestSpiInstantiator.instantiate(ArgumentConverter.class, clazz, extensionContext))
 					.map(converter -> AnnotationConsumerInitializer.initialize(declaration.getAnnotatedElement(), converter))
 					.map(Converter::new)
-					.orElseGet(() -> Converter.createDefault(extensionContext));
+					.orElse(Converter.DEFAULT);
 		} // @formatter:on
 		catch (Exception ex) {
 			throw parameterResolutionException("Error creating ArgumentConverter", ex, declaration.getParameterIndex());
@@ -479,9 +479,7 @@ Object resolve(FieldContext fieldContext, ExtensionContext extensionContext, Eva
 
 	private record Converter(ArgumentConverter argumentConverter) implements Resolver {
 
-		private static Converter createDefault(ExtensionContext context) {
-			return new Converter(new DefaultArgumentConverter(context));
-		}
+		static final Converter DEFAULT = new Converter(DefaultArgumentConverter.INSTANCE);
 
 		@Override
 		public @Nullable Object resolve(ParameterContext parameterContext, int parameterIndex,

junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessor.java

@@ -19,7 +19,6 @@
 
 import org.apiguardian.api.API;
 import org.jspecify.annotations.Nullable;
-import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.converter.DefaultArgumentConverter;
 import org.junit.platform.commons.util.ClassUtils;
 import org.junit.platform.commons.util.Preconditions;
@@ -41,13 +40,12 @@ public class DefaultArgumentsAccessor implements ArgumentsAccessor {
 	private final @Nullable Object[] arguments;
 	private final BiFunction<@Nullable Object, Class<?>, @Nullable Object> converter;
 
-	public static DefaultArgumentsAccessor create(ExtensionContext context, int invocationIndex,
-			ClassLoader classLoader, @Nullable Object[] arguments) {
+	public static DefaultArgumentsAccessor create(int invocationIndex, ClassLoader classLoader,
+			@Nullable Object[] arguments) {
 		Preconditions.notNull(classLoader, "ClassLoader must not be null");
 
 		BiFunction<@Nullable Object, Class<?>, @Nullable Object> converter = (source,
-				targetType) -> new DefaultArgumentConverter(context) //
-						.convert(source, targetType, classLoader);
+				targetType) -> DefaultArgumentConverter.INSTANCE.convert(source, targetType, classLoader);
 		return new DefaultArgumentsAccessor(converter, invocationIndex, arguments);
 	}
 

junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java

@@ -21,11 +21,9 @@
 import java.util.Currency;
 import java.util.Locale;
 import java.util.UUID;
-import java.util.function.Function;
 
 import org.apiguardian.api.API;
 import org.jspecify.annotations.Nullable;
-import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.support.FieldContext;
 import org.junit.platform.commons.support.conversion.ConversionException;
@@ -53,31 +51,9 @@
 @API(status = INTERNAL, since = "5.0")
 public class DefaultArgumentConverter implements ArgumentConverter {
 
-	/**
-	 * Property name used to set the format for the conversion of {@link Locale}
-	 * arguments: {@value}
-	 *
-	 * <h4>Supported Values</h4>
-	 * <ul>
-	 * <li>{@code bcp_47}: uses the IETF BCP 47 language tag format, delegating
-	 * the conversion to {@link Locale#forLanguageTag(String)}</li>
-	 * <li>{@code iso_639}: uses the ISO 639 alpha-2 or alpha-3 language code
-	 * format, delegating the conversion to {@link Locale#Locale(String)}</li>
-	 * </ul>
-	 *
-	 * <p>If not specified, the default is {@code bcp_47}.
-	 *
-	 * @since 5.13
-	 */
-	public static final String DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME = "junit.jupiter.params.arguments.conversion.locale.format";
-
-	private static final Function<String, LocaleConversionFormat> TRANSFORMER = value -> LocaleConversionFormat.valueOf(
-		value.strip().toUpperCase(Locale.ROOT));
-
-	private final ExtensionContext context;
-
-	public DefaultArgumentConverter(ExtensionContext context) {
-		this.context = context;
+	public static final DefaultArgumentConverter INSTANCE = new DefaultArgumentConverter();
+
+	private DefaultArgumentConverter() {
 	}
 
 	@Override
@@ -110,10 +86,6 @@ public DefaultArgumentConverter(ExtensionContext context) {
 		}
 
 		if (source instanceof String string) {
-			if (targetType == Locale.class && getLocaleConversionFormat() == LocaleConversionFormat.BCP_47) {
-				return Locale.forLanguageTag(string);
-			}
-
 			try {
 				return convert(string, targetType, classLoader);
 			}
@@ -126,22 +98,9 @@ public DefaultArgumentConverter(ExtensionContext context) {
 			source.getClass().getTypeName(), targetType.getTypeName()));
 	}
 
-	private LocaleConversionFormat getLocaleConversionFormat() {
-		return context.getConfigurationParameter(DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME, TRANSFORMER) //
-				.orElse(LocaleConversionFormat.BCP_47);
-	}
-
 	@Nullable
 	Object convert(@Nullable String source, Class<?> targetType, ClassLoader classLoader) {
 		return ConversionSupport.convert(source, targetType, classLoader);
 	}
 
-	enum LocaleConversionFormat {
-
-		BCP_47,
-
-		ISO_639
-
-	}
-
 }

junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToCommonJavaTypesConverter.java

@@ -27,7 +27,6 @@
 
 class StringToCommonJavaTypesConverter implements StringToObjectConverter {
 
-	@SuppressWarnings("deprecation")
 	private static final Map<Class<?>, Function<String, ?>> CONVERTERS = Map.of( //
 		// java.io and java.nio
 		File.class, File::new, //
@@ -38,7 +37,7 @@ class StringToCommonJavaTypesConverter implements StringToObjectConverter {
 		URL.class, StringToCommonJavaTypesConverter::toURL,
 		// java.util
 		Currency.class, Currency::getInstance, //
-		Locale.class, Locale::new, //
+		Locale.class, Locale::forLanguageTag, //
 		UUID.class, UUID::fromString //
 	);
 

jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryTests.java

@@ -269,8 +269,9 @@ void usingTheRemovedScopeConfigurationParameterProducesWarning() {
 				.configurationParameter("junit.jupiter.tempdir.scope", "per_context"));
 
 		assertThat(results.getDiscoveryIssues()) //
-				.contains(DiscoveryIssue.create(Severity.WARNING,
-					"The 'junit.jupiter.tempdir.scope' configuration parameter is no longer supported: per_context. Please remove it from your configuration."));
+				.contains(DiscoveryIssue.create(Severity.WARNING, """
+						The 'junit.jupiter.tempdir.scope' configuration parameter is no longer supported. \
+						Please remove it from your configuration."""));
 	}
 
 	@Nested

jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestIntegrationTests.java

@@ -11,6 +11,7 @@
 package org.junit.jupiter.params;
 
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.within;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -22,7 +23,6 @@
 import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS;
 import static org.junit.jupiter.engine.discovery.JupiterUniqueIdBuilder.appendTestTemplateInvocationSegment;
 import static org.junit.jupiter.engine.discovery.JupiterUniqueIdBuilder.uniqueIdForTestTemplateMethod;
-import static org.junit.jupiter.params.converter.DefaultArgumentConverter.DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME;
 import static org.junit.jupiter.params.provider.Arguments.arguments;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectIteration;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectMethod;
@@ -99,6 +99,7 @@
 import org.junit.jupiter.params.converter.ArgumentConversionException;
 import org.junit.jupiter.params.converter.ArgumentConverter;
 import org.junit.jupiter.params.converter.ConvertWith;
+import org.junit.jupiter.params.converter.TypedArgumentConverter;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.ArgumentsProvider;
 import org.junit.jupiter.params.provider.ArgumentsSource;
@@ -114,6 +115,8 @@
 import org.junit.jupiter.params.support.ParameterDeclarations;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.ClassUtils;
+import org.junit.platform.engine.DiscoveryIssue;
+import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.testkit.engine.EngineExecutionResults;
@@ -488,17 +491,20 @@ void executesWithDefaultLocaleConversionFormat() {
 	}
 
 	@Test
-	void executesWithBcp47LocaleConversionFormat() {
-		var results = execute(Map.of(DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME, "bcp_47"),
-			LocaleConversionTestCase.class, "testWithBcp47", Locale.class);
+	void emitsWarningForNoLongerSupportedConfigurationParameter() {
+		var results = discoverTests(request -> request //
+				.configurationParameter("junit.jupiter.params.arguments.conversion.locale.format", "iso_639") //
+				.selectors(selectMethod(LocaleConversionTestCase.class, "testWithBcp47", Locale.class)));
 
-		results.allEvents().assertStatistics(stats -> stats.started(4).succeeded(4));
+		assertThat(results.getDiscoveryIssues()) //
+				.contains(DiscoveryIssue.create(Severity.WARNING, """
+						The 'junit.jupiter.params.arguments.conversion.locale.format' configuration parameter \
+						is no longer supported. Please remove it from your configuration."""));
 	}
 
 	@Test
-	void executesWithIso639LocaleConversionFormat() {
-		var results = execute(Map.of(DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME, "iso_639"),
-			LocaleConversionTestCase.class, "testWithIso639", Locale.class);
+	void executesWithCustomLocalConverterUsingIso639Format() {
+		var results = execute(LocaleConversionTestCase.class, "testWithIso639", Locale.class);
 
 		results.allEvents().assertStatistics(stats -> stats.started(4).succeeded(4));
 	}
@@ -2566,11 +2572,24 @@ void testWithBcp47(Locale locale) {
 
 		@ParameterizedTest
 		@ValueSource(strings = "en-US")
-		void testWithIso639(Locale locale) {
+		void testWithIso639(@ConvertWith(Iso639Converter.class) Locale locale) {
 			assertEquals("en-us", locale.getLanguage());
 			assertEquals("", locale.getCountry());
 		}
 
+		static class Iso639Converter extends TypedArgumentConverter<String, Locale> {
+
+			Iso639Converter() {
+				super(String.class, Locale.class);
+			}
+
+			@SuppressWarnings("deprecation")
+			@Override
+			protected Locale convert(@Nullable String source) throws ArgumentConversionException {
+				return new Locale(requireNonNull(source));
+			}
+		}
+
 	}
 
 	private static class TwoSingleStringArgumentsProvider implements ArgumentsProvider {

jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessorTests.java

@@ -171,7 +171,7 @@ private static DefaultArgumentsAccessor defaultArgumentsAccessor(int invocationI
 			@Nullable Object... arguments) {
 		var context = mock(ExtensionContext.class);
 		var classLoader = DefaultArgumentsAccessorTests.class.getClassLoader();
-		return DefaultArgumentsAccessor.create(context, invocationIndex, classLoader, arguments);
+		return DefaultArgumentsAccessor.create(invocationIndex, classLoader, arguments);
 	}
 
 	@SuppressWarnings("unused")

jupiter-tests/src/test/java/org/junit/jupiter/params/converter/DefaultArgumentConverterTests.java

@@ -12,26 +12,16 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
-import static org.junit.jupiter.params.converter.DefaultArgumentConverter.DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME;
-import static org.junit.jupiter.params.converter.DefaultArgumentConverter.LocaleConversionFormat.BCP_47;
-import static org.junit.jupiter.params.converter.DefaultArgumentConverter.LocaleConversionFormat.ISO_639;
 import static org.junit.platform.commons.util.ClassLoaderUtils.getClassLoader;
 import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.doThrow;
-import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.when;
-
-import java.util.Locale;
-import java.util.Optional;
 
 import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.commons.support.ReflectionSupport;
@@ -46,8 +36,7 @@
  */
 class DefaultArgumentConverterTests {
 
-	private final ExtensionContext context = mock();
-	private final DefaultArgumentConverter underTest = spy(new DefaultArgumentConverter(context));
+	private final DefaultArgumentConverter underTest = spy(DefaultArgumentConverter.INSTANCE);
 
 	@Test
 	void isAwareOfNull() {
@@ -112,36 +101,6 @@ void delegatesStringsConversion() {
 		verify(underTest).convert("value", int.class, getClassLoader(DefaultArgumentConverterTests.class));
 	}
 
-	@Test
-	void convertsLocaleWithDefaultFormat() {
-		when(context.getConfigurationParameter(eq(DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME), any())) //
-				.thenReturn(Optional.empty());
-
-		assertConverts("en", Locale.class, Locale.ENGLISH);
-		assertConverts("en-US", Locale.class, Locale.US);
-	}
-
-	@Test
-	void convertsLocaleWithExplicitBcp47Format() {
-		when(context.getConfigurationParameter(eq(DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME), any())) //
-				.thenReturn(Optional.of(BCP_47));
-
-		assertConverts("en", Locale.class, Locale.ENGLISH);
-		assertConverts("en-US", Locale.class, Locale.US);
-	}
-
-	@Test
-	void delegatesLocaleConversionWithExplicitIso639Format() {
-		when(context.getConfigurationParameter(eq(DEFAULT_LOCALE_CONVERSION_FORMAT_PROPERTY_NAME), any())) //
-				.thenReturn(Optional.of(ISO_639));
-
-		doReturn(null).when(underTest).convert(any(), any(), any(ClassLoader.class));
-
-		convert("en", Locale.class);
-
-		verify(underTest).convert("en", Locale.class, getClassLoader(DefaultArgumentConverterTests.class));
-	}
-
 	@Test
 	void throwsExceptionForDelegatedConversionFailure() {
 		ConversionException exception = new ConversionException("fail");