Introduce ContextCustomizer API in the TestContext Framework

Allow third-parties to contribute ContextCustomizers that can customize
ApplicationContexts created by the Spring TestContext Framework (TCF)
before they are refreshed.

A customizer may be provided via a ContextCustomizerFactory which is
registered with `spring.factories`. Each factory is consulted whenever
a new ApplicationContext needs to be created by the TCF. Factories may
inspect various details about the test and either return a new
ContextCustomizer or null.

ContextCustomizers are similar to ApplicationContextInitializers and
may perform any number of tasks, including bean registration, setting
of active profiles, etc.

Issue: SPR-13998

spring-test/src/test/java/org/springframework/test/context/MergedContextConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.test.context;
 
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -28,6 +29,7 @@ import org.springframework.test.context.support.AnnotationConfigContextLoader;
 import org.springframework.test.context.support.GenericXmlContextLoader;
 
 import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
 
 /**
  * Unit tests for {@link MergedContextConfiguration}.
@@ -400,6 +402,36 @@ public class MergedContextConfigurationTests {
 		assertNotEquals(mergedConfig2, mergedConfig1);
 	}
 
+	@Test
+	public void equalsWithSameContextCustomizers() {
+		Set<ContextCustomizer> customizers1 = Collections.singleton(
+				mock(ContextCustomizer.class));
+		MergedContextConfiguration mergedConfig1 = new MergedContextConfiguration(
+				getClass(), EMPTY_STRING_ARRAY, EMPTY_CLASS_ARRAY, null,
+				EMPTY_STRING_ARRAY, null, null, customizers1, loader, null, null);
+		MergedContextConfiguration mergedConfig2 = new MergedContextConfiguration(
+				getClass(), EMPTY_STRING_ARRAY, EMPTY_CLASS_ARRAY, null,
+				EMPTY_STRING_ARRAY, null, null, customizers1, loader, null, null);
+		assertEquals(mergedConfig1, mergedConfig2);
+	}
+
+	@Test
+	public void equalsWithDifferentContextCustomizers() {
+		Set<ContextCustomizer> customizers1 = Collections.singleton(
+				mock(ContextCustomizer.class));
+		Set<ContextCustomizer> customizers2 = Collections.singleton(
+				mock(ContextCustomizer.class));
+
+		MergedContextConfiguration mergedConfig1 = new MergedContextConfiguration(
+				getClass(), EMPTY_STRING_ARRAY, EMPTY_CLASS_ARRAY, null,
+				EMPTY_STRING_ARRAY, null, null, customizers1, loader, null, null);
+		MergedContextConfiguration mergedConfig2 = new MergedContextConfiguration(
+				getClass(), EMPTY_STRING_ARRAY, EMPTY_CLASS_ARRAY, null,
+				EMPTY_STRING_ARRAY, null, null, customizers2, loader, null, null);
+		assertNotEquals(mergedConfig1, mergedConfig2);
+		assertNotEquals(mergedConfig2, mergedConfig1);
+	}
+
 	/**
 	 * @since 3.2.2
 	 */

spring-test/src/test/java/org/springframework/test/context/TestContextManagerVerifyAttributesTests.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.context;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.ConfigurableApplicationContext;
+
+import static org.hamcrest.CoreMatchers.*;
+
+/**
+ * JUnit 4 based unit test for {@link TestContextManager}, which verifies
+ * ContextConfiguration attributes are defined.
+ *
+ * @author Phillip Webb
+ * @since 4.3
+ */
+public class TestContextManagerVerifyAttributesTests {
+
+	@Rule
+	public ExpectedException expectedException = ExpectedException.none();
+
+	@Test
+	public void processContextConfigurationWithMissingContextConfigAttributes() {
+		expectedException.expect(IllegalStateException.class);
+		expectedException.expectMessage(containsString("was unable to detect defaults, "
+				+ "and no ApplicationContextInitializers or ContextCustomizers were "
+				+ "declared for context configuration"));
+		new TestContextManager(MissingContextAttributes.class);
+	}
+
+	@Test
+	public void processContextConfigurationWitListener() {
+		new TestContextManager(WithInitializer.class);
+	}
+
+
+	@ContextConfiguration
+	private static class MissingContextAttributes {
+
+	}
+
+	@ContextConfiguration(initializers=ExampleInitializer.class)
+	private static class WithInitializer {
+
+	}
+
+	static class ExampleInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
+
+		@Override
+		public void initialize(ConfigurableApplicationContext applicationContext) {
+		}
+
+	}
+}

spring-test/src/test/java/org/springframework/test/context/junit4/ContextCustomizerSpringRunnerTests.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.context.junit4;
+
+import java.util.Collections;
+import java.util.List;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.test.context.BootstrapWith;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.ContextConfigurationAttributes;
+import org.springframework.test.context.ContextCustomizer;
+import org.springframework.test.context.ContextCustomizerFactory;
+import org.springframework.test.context.MergedContextConfiguration;
+import org.springframework.test.context.junit4.ContextCustomizerSpringRunnerTests.CustomTestContextBootstrapper;
+import org.springframework.test.context.support.DefaultTestContextBootstrapper;
+
+import static org.junit.Assert.*;
+
+/**
+ * JUnit 4 based integration test which verifies support of
+ * {@link ContextCustomizerFactory} and {@link ContextCustomizer}.
+ *
+ * @author Phillip Webb
+ * @since 4.3
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@BootstrapWith(CustomTestContextBootstrapper.class)
+@ContextConfiguration
+public class ContextCustomizerSpringRunnerTests {
+
+	@Autowired
+	private MyBean myBean;
+
+	@Test
+	public void injectedMyBean() throws Exception {
+		assertNotNull(this.myBean);
+	}
+
+	public static class CustomTestContextBootstrapper
+			extends DefaultTestContextBootstrapper {
+
+		@Override
+		protected List<ContextCustomizerFactory> geContextCustomizerFactories() {
+			return Collections.singletonList(new ContextCustomizerFactory() {
+
+				@Override
+				public ContextCustomizer getContextCustomizer(Class<?> testClass,
+						List<ContextConfigurationAttributes> configurationAttributes) {
+					return new TestContextCustomizers();
+				}
+
+			});
+		}
+
+	}
+
+	public static class TestContextCustomizers implements ContextCustomizer {
+
+		@Override
+		public void customizeContext(ConfigurableApplicationContext context,
+				MergedContextConfiguration mergedContextConfiguration) {
+			context.getBeanFactory().registerSingleton("mybean", new MyBean());
+		}
+
+	}
+
+	public static class MyBean {
+	}
+
+}

spring-test/src/test/java/org/springframework/test/context/support/BootstrapTestUtilsMergedConfigTests.java

@@ -63,7 +63,7 @@ public class BootstrapTestUtilsMergedConfigTests extends AbstractContextConfigur
 	public void buildMergedConfigWithContextConfigurationWithoutLocationsClassesOrInitializers() {
 		exception.expect(IllegalStateException.class);
 		exception.expectMessage(startsWith("DelegatingSmartContextLoader was unable to detect defaults, "
-				+ "and no ApplicationContextInitializers were declared for context configuration attributes"));
+				+ "and no ApplicationContextInitializers or ContextCustomizers were declared for context configuration attribute"));
 
 		buildMergedContextConfiguration(MissingContextAttributesTestCase.class);
 	}