Demo @ContextConfiguration as composed annotation with ACI

This commit demonstrates how to register one or more @Configuration
classes via an ApplicationContextInitializer in a composed annotation so
that certain @Configuration classes are always registered whenever the
composed annotation is used, even if the composed annotation is used to
declare additional @Configuration classes.

spring-test/src/test/java/org/springframework/test/context/junit4/aci/annotation/BarConfig.java

@@ -0,0 +1,34 @@
+/*
+ * 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.aci.annotation;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * @author Sam Brannen
+ * @since 4.3
+ */
+@Configuration
+class BarConfig {
+
+	@Bean
+	String bar() {
+		return "bar";
+	}
+
+}

spring-test/src/test/java/org/springframework/test/context/junit4/aci/annotation/FooConfig.java

@@ -0,0 +1,34 @@
+/*
+ * 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.aci.annotation;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * @author Sam Brannen
+ * @since 4.3
+ */
+@Configuration
+class FooConfig {
+
+	@Bean
+	String foo() {
+		return "foo";
+	}
+
+}

spring-test/src/test/java/org/springframework/test/context/junit4/aci/annotation/InitializerConfiguredViaMetaAnnotationTests.java

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+/*
+ * 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.aci.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.util.List;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.annotation.AnnotatedBeanDefinitionReader;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.annotation.AliasFor;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.test.context.junit4.aci.annotation.InitializerConfiguredViaMetaAnnotationTests.ComposedContextConfiguration;
+import org.springframework.test.context.support.AnnotationConfigContextLoader;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Integration test that demonstrates how to register one or more {@code @Configuration}
+ * classes via an {@link ApplicationContextInitializer} in a composed annotation so
+ * that certain {@code @Configuration} classes are always registered whenever the composed
+ * annotation is used, even if the composed annotation is used to declare additional
+ * {@code @Configuration} classes.
+ *
+ * <p>This class has been implemented in response to the following Stack Overflow question:
+ * <a href="http://stackoverflow.com/questions/35733344/can-contextconfiguration-in-a-custom-annotation-be-merged">
+ * Can {@code @ContextConfiguration} in a custom annotation be merged?</a>
+ *
+ * @author Sam Brannen
+ * @since 4.3
+ */
+@RunWith(SpringRunner.class)
+@ComposedContextConfiguration(BarConfig.class)
+public class InitializerConfiguredViaMetaAnnotationTests {
+
+	@Autowired
+	String foo;
+
+	@Autowired
+	String bar;
+
+	@Autowired
+	List<String> strings;
+
+
+	@Test
+	public void beansFromInitializerAndComposedAnnotation() {
+		assertEquals(2, strings.size());
+		assertEquals("foo", foo);
+		assertEquals("bar", bar);
+	}
+
+
+	static class FooConfigInitializer implements ApplicationContextInitializer<GenericApplicationContext> {
+
+		@Override
+		public void initialize(GenericApplicationContext applicationContext) {
+			new AnnotatedBeanDefinitionReader(applicationContext).register(FooConfig.class);
+		}
+	}
+
+	@ContextConfiguration(loader = AnnotationConfigContextLoader.class, initializers = FooConfigInitializer.class)
+	@Retention(RetentionPolicy.RUNTIME)
+	@Target(ElementType.TYPE)
+	@interface ComposedContextConfiguration {
+
+		@AliasFor(annotation = ContextConfiguration.class, attribute = "classes")
+		Class<?>[] value() default {};
+	}
+
+}