Apply initializer automatically for context tests

Update `ServiceConnectionContextCustomizer` so that is applies the
`TestcontainersLifecycleApplicationContextInitializer` to all
application contexts.

Closes gh-35222

spring-boot-project/spring-boot-testcontainers/src/main/java/org/springframework/boot/testcontainers/lifecycle/TestcontainersLifecycleApplicationContextInitializer.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.testcontainers.lifecycle;
 
+import java.util.WeakHashMap;
+
 import org.testcontainers.lifecycle.Startable;
 
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
@@ -32,8 +34,15 @@ import org.springframework.context.ConfigurableApplicationContext;
 public class TestcontainersLifecycleApplicationContextInitializer
 		implements ApplicationContextInitializer<ConfigurableApplicationContext> {
 
+	private static WeakHashMap<ConfigurableApplicationContext, Boolean> applied = new WeakHashMap<>();
+
 	@Override
 	public void initialize(ConfigurableApplicationContext applicationContext) {
+		synchronized (applied) {
+			if (applied.put(applicationContext, Boolean.TRUE) == Boolean.TRUE) {
+				return;
+			}
+		}
 		ConfigurableListableBeanFactory beanFactory = applicationContext.getBeanFactory();
 		applicationContext.addBeanFactoryPostProcessor(new TestcontainersLifecycleBeanFactoryPostProcessor());
 		beanFactory.addBeanPostProcessor(new TestcontainersLifecycleBeanPostProcessor(beanFactory));

spring-boot-project/spring-boot-testcontainers/src/main/java/org/springframework/boot/testcontainers/service/connection/ServiceConnectionContextCustomizer.java

@@ -26,6 +26,7 @@ import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.boot.autoconfigure.service.connection.ConnectionDetails;
 import org.springframework.boot.autoconfigure.service.connection.ConnectionDetailsFactories;
+import org.springframework.boot.testcontainers.lifecycle.TestcontainersLifecycleApplicationContextInitializer;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.test.context.ContextCustomizer;
 import org.springframework.test.context.MergedContextConfiguration;
@@ -58,6 +59,7 @@ class ServiceConnectionContextCustomizer implements ContextCustomizer {
 
 	@Override
 	public void customizeContext(ConfigurableApplicationContext context, MergedContextConfiguration mergedConfig) {
+		new TestcontainersLifecycleApplicationContextInitializer().initialize(context);
 		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
 		if (beanFactory instanceof BeanDefinitionRegistry registry) {
 			new ConnectionDetailsRegistrar(beanFactory, this.connectionDetailsFactories)

spring-boot-project/spring-boot-testcontainers/src/main/java/org/springframework/boot/testcontainers/service/connection/ServiceConnectionContextCustomizerFactory.java

@@ -49,7 +49,7 @@ class ServiceConnectionContextCustomizerFactory implements ContextCustomizerFact
 			List<ContextConfigurationAttributes> configAttributes) {
 		List<ContainerConnectionSource<?>> sources = new ArrayList<>();
 		findSources(testClass, sources);
-		return (sources.isEmpty()) ? null : new ServiceConnectionContextCustomizer(sources);
+		return new ServiceConnectionContextCustomizer(sources);
 	}
 
 	private void findSources(Class<?> clazz, List<ContainerConnectionSource<?>> sources) {

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/lifecycle/TestcontainersLifecycleApplicationContextInitializerTests.java

@@ -24,6 +24,7 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.BDDMockito.then;
 import static org.mockito.Mockito.mock;
@@ -84,6 +85,16 @@ class TestcontainersLifecycleApplicationContextInitializerTests {
 		then(container).should(never()).close();
 	}
 
+	@Test
+	void doesNotInitializeSameContextMoreThanOnce() {
+		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
+		int initialNumberOfPostProcessors = applicationContext.getBeanFactoryPostProcessors().size();
+		for (int i = 0; i < 10; i++) {
+			new TestcontainersLifecycleApplicationContextInitializer().initialize(applicationContext);
+		}
+		assertThat(applicationContext.getBeanFactoryPostProcessors()).hasSize(initialNumberOfPostProcessors + 1);
+	}
+
 	private AnnotationConfigApplicationContext createApplicationContext(Startable container) {
 		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
 		new TestcontainersLifecycleApplicationContextInitializer().initialize(applicationContext);

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/service/connection/ServiceConnectionContextCustomizerFactoryTests.java

@@ -24,8 +24,13 @@ import org.junit.jupiter.api.Test;
 import org.testcontainers.containers.Container;
 import org.testcontainers.containers.GenericContainer;
 
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.test.context.ContextCustomizer;
+import org.springframework.test.context.MergedContextConfiguration;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link ServiceConnectionContextCustomizerFactory}.
@@ -39,8 +44,14 @@ class ServiceConnectionContextCustomizerFactoryTests {
 	private final ServiceConnectionContextCustomizerFactory factory = new ServiceConnectionContextCustomizerFactory();
 
 	@Test
-	void createContextCustomizerWhenNoServiceConnectionsReturnsNull() {
-		assertThat(this.factory.createContextCustomizer(NoServiceConnections.class, null)).isNull();
+	void createContextCustomizerWhenNoServiceConnectionsReturnsCustomizerToApplyInitializer() {
+		ContextCustomizer customizer = this.factory.createContextCustomizer(NoServiceConnections.class, null);
+		assertThat(customizer).isNotNull();
+		GenericApplicationContext context = new GenericApplicationContext();
+		int initialNumberOfPostProcessors = context.getBeanFactoryPostProcessors().size();
+		MergedContextConfiguration mergedConfig = mock(MergedContextConfiguration.class);
+		customizer.customizeContext(context, mergedConfig);
+		assertThat(context.getBeanFactoryPostProcessors()).hasSize(initialNumberOfPostProcessors + 1);
 	}
 
 	@Test