Add TestContextApplicationEventPublisherAdapter class adapting the Spring TestContext framework and API as an instance of the ApplicationEventPublisher interface.

spring-data-geode-test/src/main/java/org/springframework/data/gemfire/tests/extensions/spring/test/context/TestContextApplicationEventPublisherAdapter.java

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+/*
+ *  Copyright 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.
+ *  You may obtain a copy of the License at
+ *
+ *       https://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.data.gemfire.tests.extensions.spring.test.context;
+
+import java.util.Optional;
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.lang.NonNull;
+import org.springframework.test.context.TestContext;
+import org.springframework.util.Assert;
+
+/**
+ * {@literal Adapter} used to adapt the {@link TestContext} API as an {@link ApplicationEventPublisher}.
+ *
+ * @author John Blum
+ * @see org.springframework.context.ApplicationEventPublisher
+ * @see org.springframework.test.context.TestContext
+ * @since 0.0.23
+ */
+@SuppressWarnings("unused")
+public class TestContextApplicationEventPublisherAdapter implements ApplicationEventPublisher {
+
+	protected static @NonNull TestContextApplicationEventPublisherAdapter from(@NonNull TestContext testContext) {
+		return new TestContextApplicationEventPublisherAdapter(testContext);
+	}
+
+	private final TestContext testContext;
+
+	/**
+	 * Constructs a new instance of {@link TestContextApplicationEventPublisherAdapter} initialized with the given,
+	 * required {@link TestContext}.
+	 *
+	 * @param testContext Spring {@link TestContext} to be adapted as a Spring {@link ApplicationEventPublisher}.
+	 * @throws IllegalArgumentException if {@link TestContext} is {@literal null}.
+	 * @see org.springframework.test.context.TestContext
+	 */
+	protected TestContextApplicationEventPublisherAdapter(@NonNull TestContext testContext) {
+		Assert.notNull(testContext, "TestContext must not be null");
+		this.testContext = testContext;
+	}
+
+	/**
+	 * Returns a reference to the configured {@link TestContext}.
+	 *
+	 * @return a reference to the configured {@link TestContext}; never {@literal null}.
+	 * @see org.springframework.test.context.TestContext
+	 */
+	protected @NonNull TestContext getTestContext() {
+		return this.testContext;
+	}
+
+	/**
+	 * Returns an {@link Optional} reference to the {@link ApplicationEventPublisher} if available.
+	 *
+	 * The {@link ApplicationEventPublisher}, or rather Spring {@link ApplicationContext}, is resolved from
+	 * the {@link TestContext} depending on whether the {@link ApplicationContext} has been initialized yet.
+	 *
+	 * @return an {@link Optional} reference to the {@link ApplicationEventPublisher} if available.
+	 * @see org.springframework.context.ApplicationEventPublisher
+	 * @see java.util.Optional
+	 * @see #getTestContext()
+	 */
+	protected Optional<ApplicationEventPublisher> getApplicationEventPublisher() {
+
+		return Optional.ofNullable(getTestContext())
+			.filter(TestContext::hasApplicationContext)
+			.map(TestContext::getApplicationContext);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	@Override
+	public void publishEvent(@NonNull Object event) {
+		getApplicationEventPublisher().ifPresent(applicationEventPublisher ->
+			applicationEventPublisher.publishEvent(event));
+	}
+}