Add new interfaces to extend DefaultLocale and DefaultTimeZone

src/main/java/org/junitpioneer/jupiter/DefaultLocale.java

@@ -103,4 +103,11 @@
 	 */
 	String variant() default "";
 
+	/**
+	 * A class implementing {@link LocaleProvider} to be used for custom {@code Locale} resolution.
+	 * This is mutually exclusive with other properties, if any other property is given a value it
+	 * will result in an {@link org.junit.jupiter.api.extension.ExtensionConfigurationException}.
+	 */
+	Class<? extends LocaleProvider> localeProvider() default LocaleProvider.NullLocaleProvider.class;
+
 }

src/main/java/org/junitpioneer/jupiter/DefaultLocaleExtension.java

@@ -17,8 +17,10 @@
 import org.junit.jupiter.api.extension.ExtensionConfigurationException;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ExtensionContext.Namespace;
+import org.junit.platform.commons.support.ReflectionSupport;
 import org.junitpioneer.internal.PioneerAnnotationUtils;
 import org.junitpioneer.internal.PioneerUtils;
+import org.junitpioneer.jupiter.LocaleProvider.NullLocaleProvider;
 
 class DefaultLocaleExtension implements BeforeEachCallback, AfterEachCallback {
 
@@ -49,20 +51,26 @@ private void storeDefaultLocale(ExtensionContext context) {
 	private static Locale createLocale(DefaultLocale annotation) {
 		if (!annotation.value().isEmpty()) {
 			return createFromLanguageTag(annotation);
-		} else {
+		} else if (!annotation.language().isEmpty()) {
 			return createFromParts(annotation);
+		} else {
+			return getFromProvider(annotation);
 		}
 	}
 
 	private static Locale createFromLanguageTag(DefaultLocale annotation) {
-		if (!annotation.language().isEmpty() || !annotation.country().isEmpty() || !annotation.variant().isEmpty()) {
+		if (!annotation.language().isEmpty() || !annotation.country().isEmpty() || !annotation.variant().isEmpty()
+				|| annotation.localeProvider() != NullLocaleProvider.class) {
 			throw new ExtensionConfigurationException(
-				"@DefaultLocale can only be used with language tag if language, country, and variant are not set");
+				"@DefaultLocale can only be used with language tag if language, country, variant and provider are not set");
 		}
 		return Locale.forLanguageTag(annotation.value());
 	}
 
 	private static Locale createFromParts(DefaultLocale annotation) {
+		if (annotation.localeProvider() != NullLocaleProvider.class)
+			throw new ExtensionConfigurationException(
+				"@DefaultLocale can only be used with language tag if provider is not set");
 		String language = annotation.language();
 		String country = annotation.country();
 		String variant = annotation.variant();
@@ -75,8 +83,28 @@ private static Locale createFromParts(DefaultLocale annotation) {
 		} else {
 			throw new ExtensionConfigurationException(
 				"@DefaultLocale not configured correctly. When not using a language tag, specify either"
-						+ "language, or language and country, or language and country and variant.");
+						+ " language, or language and country, or language and country and variant.");
+		}
+	}
+
+	private static Locale getFromProvider(DefaultLocale annotation) {
+		if (!annotation.value().isEmpty() || !annotation.language().isEmpty() || !annotation.country().isEmpty()
+				|| !annotation.variant().isEmpty())
+			throw new ExtensionConfigurationException(
+				"@DefaultLocale can only be used with a provider if value, language, country and variant are not set.");
+		var providerClass = annotation.localeProvider();
+		LocaleProvider provider;
+		try {
+			provider = ReflectionSupport.newInstance(providerClass);
+		}
+		catch (Exception exception) {
+			throw new ExtensionConfigurationException(
+				"LocaleProvider instance could not be constructed because of an exception", exception);
 		}
+		var locale = provider.get();
+		if (locale == null)
+			throw new NullPointerException("LocaleProvider instance returned with null");
+		return locale;
 	}
 
 	@Override

src/main/java/org/junitpioneer/jupiter/DefaultTimeZone.java

@@ -62,6 +62,13 @@
 	 * "GMT-8:00". Note that the support of abbreviations is for JDK 1.1.x
 	 * compatibility only and full names should be used.
 	 */
-	String value();
+	String value() default "";
+
+	/**
+	 * A class implementing {@link TimeZoneProvider} to be used for custom {@code TimeZone} resolution.
+	 * This is mutually exclusive with other properties, if any other property is given a value it
+	 * will result in an {@link org.junit.jupiter.api.extension.ExtensionConfigurationException}.
+	 */
+	Class<? extends TimeZoneProvider> timeZoneProvider() default TimeZoneProvider.NullTimeZoneProvider.class;
 
 }

src/main/java/org/junitpioneer/jupiter/DefaultTimeZoneExtension.java

@@ -10,6 +10,7 @@
 
 package org.junitpioneer.jupiter;
 
+import java.util.Optional;
 import java.util.TimeZone;
 
 import org.junit.jupiter.api.extension.AfterEachCallback;
@@ -18,7 +19,9 @@
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ExtensionContext.Namespace;
 import org.junit.jupiter.api.extension.ExtensionContext.Store;
+import org.junit.platform.commons.support.ReflectionSupport;
 import org.junitpioneer.internal.PioneerAnnotationUtils;
+import org.junitpioneer.jupiter.TimeZoneProvider.NullTimeZoneProvider;
 
 class DefaultTimeZoneExtension implements BeforeEachCallback, AfterEachCallback {
 
@@ -34,14 +37,28 @@ public void beforeEach(ExtensionContext context) {
 	}
 
 	private void setDefaultTimeZone(Store store, DefaultTimeZone annotation) {
-		TimeZone defaultTimeZone = createTimeZone(annotation.value());
+		validateCorrectConfiguration(annotation);
+		TimeZone defaultTimeZone;
+		if (annotation.timeZoneProvider() != NullTimeZoneProvider.class)
+			defaultTimeZone = createTimeZone(annotation.timeZoneProvider());
+		else
+			defaultTimeZone = createTimeZone(annotation.value());
 		// defer storing the current default time zone until the new time zone could be created from the configuration
 		// (this prevents cases where misconfigured extensions store default time zone now and restore it later,
 		// which leads to race conditions in our tests)
 		storeDefaultTimeZone(store);
 		TimeZone.setDefault(defaultTimeZone);
 	}
 
+	private static void validateCorrectConfiguration(DefaultTimeZone annotation) {
+		boolean noValue = annotation.value().isEmpty();
+		boolean noProvider = annotation.timeZoneProvider() == NullTimeZoneProvider.class;
+		if (noValue == noProvider)
+			throw new ExtensionConfigurationException(
+				"Either a valid time zone id or a TimeZoneProvider must be provided to "
+						+ DefaultTimeZone.class.getSimpleName());
+	}
+
 	private static TimeZone createTimeZone(String timeZoneId) {
 		TimeZone configuredTimeZone = TimeZone.getTimeZone(timeZoneId);
 		// TimeZone::getTimeZone returns with GMT as fallback if the given ID cannot be understood
@@ -55,6 +72,17 @@ private static TimeZone createTimeZone(String timeZoneId) {
 		return configuredTimeZone;
 	}
 
+	private static TimeZone createTimeZone(Class<? extends TimeZoneProvider> providerClass) {
+		try {
+			TimeZoneProvider provider = ReflectionSupport.newInstance(providerClass);
+			return Optional.ofNullable(provider.get()).orElse(TimeZone.getTimeZone("GMT"));
+		}
+		catch (Exception exception) {
+			throw new ExtensionConfigurationException("Could not instantiate TimeZoneProvider because of exception",
+				exception);
+		}
+	}
+
 	private void storeDefaultTimeZone(Store store) {
 		store.put(KEY, TimeZone.getDefault());
 	}

src/main/java/org/junitpioneer/jupiter/LocaleProvider.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2016-2023 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * http://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junitpioneer.jupiter;
+
+import java.util.Locale;
+import java.util.function.Supplier;
+
+public interface LocaleProvider extends Supplier<Locale> {
+
+	interface NullLocaleProvider extends LocaleProvider {
+	}
+
+}

src/main/java/org/junitpioneer/jupiter/TimeZoneProvider.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2016-2023 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * http://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junitpioneer.jupiter;
+
+import java.util.TimeZone;
+import java.util.function.Supplier;
+
+public interface TimeZoneProvider extends Supplier<TimeZone> {
+
+	interface NullTimeZoneProvider extends TimeZoneProvider {
+	}
+
+}

src/test/java/org/junitpioneer/jupiter/DefaultLocaleTests.java

@@ -183,15 +183,15 @@ void setForTestMethod() {
 			}
 
 			@AfterAll
-			@ReadsDefaultTimeZone
+			@ReadsDefaultLocale
 			void resetAfterTestMethodExecution() {
 				assertThat(Locale.getDefault().getLanguage()).isEqualTo("custom");
 			}
 
 		}
 
 		@AfterAll
-		@ReadsDefaultTimeZone
+		@ReadsDefaultLocale
 		void resetAfterTestMethodExecution() {
 			assertThat(Locale.getDefault().getLanguage()).isEqualTo("custom");
 		}
@@ -364,4 +364,120 @@ static class InheritanceBaseTest {
 
 	}
 
+	@Nested
+	@DisplayName("when used with a locale provider")
+	class LocaleProviderTests {
+
+		@Test
+		@DisplayName("can get a basic locale from provider")
+		@DefaultLocale(localeProvider = BasicLocaleProvider.class)
+		void canUseProvider() {
+			assertThat(Locale.getDefault()).isEqualTo(Locale.FRENCH);
+		}
+
+		@Test
+		@ReadsDefaultLocale
+		@DisplayName("throws a NullPointerException with custom message if provider returns null")
+		void providerReturnsNull() {
+			ExecutionResults results = executeTestMethod(BadProviderTestCases.class, "returnsNull");
+
+			assertThat(results)
+					.hasSingleFailedTest()
+					.withExceptionInstanceOf(NullPointerException.class)
+					.hasMessageContaining("LocaleProvider instance returned with null");
+		}
+
+		@Test
+		@ReadsDefaultLocale
+		@DisplayName("throws an ExtensionConfigurationException if any other option is present")
+		void mutuallyExclusiveWithValue() {
+			ExecutionResults results = executeTestMethod(BadProviderTestCases.class, "mutuallyExclusiveWithValue");
+
+			assertThat(results)
+					.hasSingleFailedTest()
+					.withExceptionInstanceOf(ExtensionConfigurationException.class)
+					.hasMessageContaining(
+						"can only be used with language tag if language, country, variant and provider are not set");
+		}
+
+		@Test
+		@ReadsDefaultLocale
+		@DisplayName("throws an ExtensionConfigurationException if any other option is present")
+		void mutuallyExclusiveWithLanguage() {
+			ExecutionResults results = executeTestMethod(BadProviderTestCases.class, "mutuallyExclusiveWithLanguage");
+
+			assertThat(results)
+					.hasSingleFailedTest()
+					.withExceptionInstanceOf(ExtensionConfigurationException.class)
+					.hasMessageContaining("can only be used with language tag if provider is not set");
+		}
+
+		@Test
+		@ReadsDefaultLocale
+		@DisplayName("throws an ExtensionConfigurationException if localeProvider can't be constructed")
+		void badConstructor() {
+			ExecutionResults results = executeTestMethod(BadProviderTestCases.class, "badConstructor");
+
+			assertThat(results)
+					.hasSingleFailedTest()
+					.withExceptionInstanceOf(ExtensionConfigurationException.class)
+					.hasMessageContaining("could not be constructed because of an exception");
+		}
+
+	}
+
+	static class BadProviderTestCases {
+
+		@Test
+		@DefaultLocale(value = "en", localeProvider = BasicLocaleProvider.class)
+		void mutuallyExclusiveWithValue() {
+		}
+
+		@Test
+		@DefaultLocale(language = "en", localeProvider = BasicLocaleProvider.class)
+		void mutuallyExclusiveWithLanguage() {
+		}
+
+		@Test
+		@DefaultLocale(localeProvider = ReturnsNullLocaleProvider.class)
+		void returnsNull() {
+		}
+
+		@Test
+		@DefaultLocale(localeProvider = BadConstructorLocaleProvider.class)
+		void badConstructor() {
+		}
+
+	}
+
+	static class BasicLocaleProvider implements LocaleProvider {
+
+		@Override
+		public Locale get() {
+			return Locale.FRENCH;
+		}
+
+	}
+
+	static class ReturnsNullLocaleProvider implements LocaleProvider {
+
+		@Override
+		public Locale get() {
+			return null;
+		}
+
+	}
+
+	static class BadConstructorLocaleProvider implements LocaleProvider {
+
+		BadConstructorLocaleProvider(String unused) {
+		}
+
+		@Override
+		public Locale get() {
+			return Locale.GERMAN;
+		}
+
+	}
+
 }