Add support to query if ApplicationContext is available in the TCF

This commit introduces support in the Spring TestContext Framework
(TCF) to query whether the test's ApplicationContext is available.

Specifically, this commit introduces the following two `default`
methods along with corresponding implementations in DefaultTestContext
and DefaultCacheAwareContextLoaderDelegate.

- `boolean hasApplicationContext()` in the TestContext API

- `boolean isContextLoaded(MergedContextConfiguration)` in the
  CacheAwareContextLoaderDelegate API

Closes gh-22756

spring-test/src/main/java/org/springframework/test/context/CacheAwareContextLoaderDelegate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -36,6 +36,30 @@ import org.springframework.test.annotation.DirtiesContext.HierarchyMode;
  */
 public interface CacheAwareContextLoaderDelegate {
 
+	/**
+	 * Determine if the {@linkplain ApplicationContext application context} for
+	 * the supplied {@link MergedContextConfiguration} has been loaded (i.e.,
+	 * is present in the {@code ContextCache}).
+	 * <p>Implementations of this method <strong>must not</strong> load the
+	 * application context as a side effect. In addition, implementations of
+	 * this method should not log the cache statistics via
+	 * {@link org.springframework.test.context.cache.ContextCache#logStatistics()}.
+	 * <p>The default implementation of this method always returns {@code false}.
+	 * Custom {@code CacheAwareContextLoaderDelegate} implementations are
+	 * therefore highly encouraged to override this method with a more meaningful
+	 * implementation. Note that the standard {@code CacheAwareContextLoaderDelegate}
+	 * implementation in Spring overrides this method appropriately.
+	 * @param mergedContextConfiguration the merged context configuration used
+	 * to load the application context; never {@code null}
+	 * @return {@code true} if the the application context has been loaded
+	 * @since 5.2
+	 * @see #loadContext
+	 * @see #closeContext
+	 */
+	default boolean isContextLoaded(MergedContextConfiguration mergedContextConfiguration) {
+		return false;
+	}
+
 	/**
 	 * Load the {@linkplain ApplicationContext application context} for the supplied
 	 * {@link MergedContextConfiguration} by delegating to the {@link ContextLoader}
@@ -49,6 +73,8 @@ public interface CacheAwareContextLoaderDelegate {
 	 * @return the application context (never {@code null})
 	 * @throws IllegalStateException if an error occurs while retrieving or loading
 	 * the application context
+	 * @see #isContextLoaded
+	 * @see #closeContext
 	 */
 	ApplicationContext loadContext(MergedContextConfiguration mergedContextConfiguration);
 
@@ -69,6 +95,8 @@ public interface CacheAwareContextLoaderDelegate {
 	 * @param hierarchyMode the hierarchy mode; may be {@code null} if the context
 	 * is not part of a hierarchy
 	 * @since 4.1
+	 * @see #isContextLoaded
+	 * @see #loadContext
 	 */
 	void closeContext(MergedContextConfiguration mergedContextConfiguration, @Nullable HierarchyMode hierarchyMode);
 

spring-test/src/main/java/org/springframework/test/context/TestContext.java

@@ -41,8 +41,28 @@ import org.springframework.test.annotation.DirtiesContext.HierarchyMode;
  * @see TestContextManager
  * @see TestExecutionListener
  */
+// Suppression required due to bug in javac in Java 8: presence of default method in a Serializable interface
+@SuppressWarnings("serial")
 public interface TestContext extends AttributeAccessor, Serializable {
 
+	/**
+	 * Determine if the {@linkplain ApplicationContext application context} for
+	 * this test context is known to be available.
+	 * <p>If this method returns {@code true}, a subsequent invocation of
+	 * {@link #getApplicationContext()} should succeed.
+	 * <p>The default implementation of this method always returns {@code false}.
+	 * Custom {@code TestContext} implementations are therefore highly encouraged
+	 * to override this method with a more meaningful implementation. Note that
+	 * the standard {@code TestContext} implementation in Spring overrides this
+	 * method appropriately.
+	 * @return {@code true} if the application context has already been loaded
+	 * @since 5.2
+	 * @see #getApplicationContext()
+	 */
+	default boolean hasApplicationContext() {
+		return false;
+	}
+
 	/**
 	 * Get the {@linkplain ApplicationContext application context} for this
 	 * test context, possibly cached.
@@ -52,6 +72,7 @@ public interface TestContext extends AttributeAccessor, Serializable {
 	 * @return the application context (never {@code null})
 	 * @throws IllegalStateException if an error occurs while retrieving the
 	 * application context
+	 * @see #hasApplicationContext()
 	 */
 	ApplicationContext getApplicationContext();
 

spring-test/src/main/java/org/springframework/test/context/cache/DefaultCacheAwareContextLoaderDelegate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -31,7 +31,7 @@ import org.springframework.util.Assert;
 /**
  * Default implementation of the {@link CacheAwareContextLoaderDelegate} interface.
  *
- * <p>To use a static {@code DefaultContextCache}, invoke the
+ * <p>To use a static {@link DefaultContextCache}, invoke the
  * {@link #DefaultCacheAwareContextLoaderDelegate()} constructor; otherwise,
  * invoke the {@link #DefaultCacheAwareContextLoaderDelegate(ContextCache)}
  * and provide a custom {@link ContextCache} implementation.
@@ -108,6 +108,13 @@ public class DefaultCacheAwareContextLoaderDelegate implements CacheAwareContext
 		return applicationContext;
 	}
 
+	@Override
+	public boolean isContextLoaded(MergedContextConfiguration mergedContextConfiguration) {
+		synchronized (this.contextCache) {
+			return this.contextCache.contains(mergedContextConfiguration);
+		}
+	}
+
 	@Override
 	public ApplicationContext loadContext(MergedContextConfiguration mergedContextConfiguration) {
 		synchronized (this.contextCache) {

spring-test/src/main/java/org/springframework/test/context/support/DefaultTestContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -95,13 +95,27 @@ public class DefaultTestContext implements TestContext {
 		this.cacheAwareContextLoaderDelegate = cacheAwareContextLoaderDelegate;
 	}
 
+	/**
+	 * Determine if the {@linkplain ApplicationContext application context} for
+	 * this test context is present in the context cache.
+	 * @return {@code true} if the application context has already been loaded
+	 * and stored in the context cache
+	 * @since 5.2
+	 * @see #getApplicationContext()
+	 * @see CacheAwareContextLoaderDelegate#isContextLoaded
+	 */
+	@Override
+	public boolean hasApplicationContext() {
+		return this.cacheAwareContextLoaderDelegate.isContextLoaded(this.mergedContextConfiguration);
+	}
+
 	/**
 	 * Get the {@linkplain ApplicationContext application context} for this
 	 * test context.
 	 * <p>The default implementation delegates to the {@link CacheAwareContextLoaderDelegate}
 	 * that was supplied when this {@code TestContext} was constructed.
 	 * @throws IllegalStateException if the context returned by the context
-	 * loader delegate is not <em>active</em> (i.e., has been closed).
+	 * loader delegate is not <em>active</em> (i.e., has been closed)
 	 * @see CacheAwareContextLoaderDelegate#loadContext
 	 */
 	public ApplicationContext getApplicationContext() {