diff --git a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientBuilderCustomizer.java b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientBuilderCustomizer.java
index 7cd12f2da2b..e40b503c25c 100644
--- a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientBuilderCustomizer.java
+++ b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientBuilderCustomizer.java
@@ -18,13 +18,12 @@ package org.springframework.boot.test.web.reactive.client;
 
 import org.springframework.context.ApplicationContext;
 import org.springframework.test.web.reactive.server.WebTestClient;
-import org.springframework.test.web.reactive.server.WebTestClient.Builder;
 
 /**
- * A customizer that can be implemented by beans wishing to customize the {@link Builder}
- * to fine-tune its auto-configuration before a {@link WebTestClient} is created.
- * Implementations can be registered in the {@link ApplicationContext} or
- * {@code spring.factories}.
+ * A customizer that can be implemented by beans wishing to customize the
+ * {@link WebTestClient.Builder} to fine-tune its auto-configuration before a
+ * {@link WebTestClient} is created. Implementations can be registered in the
+ * {@link ApplicationContext} or {@code spring.factories}.
  *
  * @author Andy Wilkinson
  * @since 4.0.0
@@ -36,6 +35,6 @@ public interface WebTestClientBuilderCustomizer {
 	 * Customize the given {@code builder}.
 	 * @param builder the builder
 	 */
-	void customize(Builder builder);
+	void customize(WebTestClient.Builder builder);
 
 }
diff --git a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizer.java b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizer.java
index d6729722357..e4376808fab 100644
--- a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizer.java
+++ b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizer.java
@@ -123,10 +123,6 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 			}
 		}
 
-		@Override
-		public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
-		}
-
 	}
 
 	/**
@@ -143,11 +139,6 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 			this.applicationContext = applicationContext;
 		}
 
-		@Override
-		public boolean isSingleton() {
-			return true;
-		}
-
 		@Override
 		public Class<?> getObjectType() {
 			return WebTestClient.class;
@@ -164,7 +155,7 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 		private WebTestClient createWebTestClient() {
 			Assert.state(this.applicationContext != null, "ApplicationContext not injected");
 			WebTestClient.Builder builder = WebTestClient.bindToServer();
-			customizeWebTestClientBuilder(builder, this.applicationContext);
+			customizeWebTestClientBuilder(builder);
 			BaseUrl baseUrl = new BaseUrlProviders(this.applicationContext).getBaseUrl();
 			if (baseUrl != null) {
 				builder.baseUrl(baseUrl.resolve());
@@ -172,7 +163,7 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 			return builder.build();
 		}
 
-		private void customizeWebTestClientBuilder(WebTestClient.Builder clientBuilder, ApplicationContext context) {
+		private void customizeWebTestClientBuilder(WebTestClient.Builder clientBuilder) {
 			Assert.state(this.applicationContext != null, "ApplicationContext not injected");
 			getWebTestClientBuilderCustomizers(this.applicationContext)
 				.forEach((customizer) -> customizer.customize(clientBuilder));
@@ -180,10 +171,9 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 
 		private List<WebTestClientBuilderCustomizer> getWebTestClientBuilderCustomizers(ApplicationContext context) {
 			List<WebTestClientBuilderCustomizer> customizers = new ArrayList<>();
-			SpringFactoriesLoader.forDefaultResourceLocation(context.getClassLoader())
-				.load(WebTestClientBuilderCustomizer.class, ArgumentResolver.of(ApplicationContext.class, context))
-				.forEach(customizers::add);
-			context.getBeansOfType(WebTestClientBuilderCustomizer.class).values().forEach(customizers::add);
+			customizers.addAll(SpringFactoriesLoader.forDefaultResourceLocation(context.getClassLoader())
+				.load(WebTestClientBuilderCustomizer.class, ArgumentResolver.of(ApplicationContext.class, context)));
+			customizers.addAll(context.getBeansOfType(WebTestClientBuilderCustomizer.class).values());
 			return customizers;
 		}
 
diff --git a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientBuilderCustomizer.java b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientBuilderCustomizer.java
index 442f2fc3bb4..47915c284d7 100644
--- a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientBuilderCustomizer.java
+++ b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientBuilderCustomizer.java
@@ -18,13 +18,12 @@ package org.springframework.boot.test.web.servlet.client;
 
 import org.springframework.context.ApplicationContext;
 import org.springframework.test.web.servlet.client.RestTestClient;
-import org.springframework.test.web.servlet.client.RestTestClient.Builder;
 
 /**
- * A customizer that can be implemented by beans wishing to customize the {@link Builder}
- * to fine-tune its auto-configuration before a {@link RestTestClient} is created.
- * Implementations can be registered in the {@link ApplicationContext} or
- * {@code spring.factories}.
+ * A customizer that can be implemented by beans wishing to customize the
+ * {@link RestTestClient.Builder} to fine-tune its auto-configuration before a
+ * {@link RestTestClient} is created. Implementations can be registered in the
+ * {@link ApplicationContext} or {@code spring.factories}.
  *
  * @author Stephane Nicoll
  * @since 4.0.0
@@ -33,9 +32,9 @@ import org.springframework.test.web.servlet.client.RestTestClient.Builder;
 public interface RestTestClientBuilderCustomizer {
 
 	/**
-	 * Customize the given {@link Builder Builder}.
+	 * Customize the given {@link RestTestClient.Builder Builder}.
 	 * @param builder the builder
 	 */
-	void customize(Builder<?> builder);
+	void customize(RestTestClient.Builder<?> builder);
 
 }
diff --git a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizer.java b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizer.java
index 405a3c58975..931b974b344 100644
--- a/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizer.java
+++ b/core/spring-boot-test/src/main/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizer.java
@@ -125,10 +125,6 @@ class RestTestClientContextCustomizer implements ContextCustomizer {
 
 		}
 
-		@Override
-		public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
-		}
-
 	}
 
 	/**
@@ -145,11 +141,6 @@ class RestTestClientContextCustomizer implements ContextCustomizer {
 			this.applicationContext = applicationContext;
 		}
 
-		@Override
-		public boolean isSingleton() {
-			return true;
-		}
-
 		@Override
 		public Class<?> getObjectType() {
 			return RestTestClient.class;
@@ -166,13 +157,12 @@ class RestTestClientContextCustomizer implements ContextCustomizer {
 		private RestTestClient createRestTestClient() {
 			Assert.state(this.applicationContext != null, "ApplicationContext not injected");
 			RestTestClient.Builder<?> builder = RestTestClient.bindToServer();
-			customizeRestTestClientBuilder(builder, this.applicationContext);
+			customizeRestTestClientBuilder(builder);
 			BaseUrl baseUrl = new BaseUrlProviders(this.applicationContext).getBaseUrl();
 			return builder.uriBuilderFactory(BaseUrlUriBuilderFactory.get(baseUrl)).build();
 		}
 
-		private void customizeRestTestClientBuilder(RestTestClient.Builder<?> clientBuilder,
-				ApplicationContext context) {
+		private void customizeRestTestClientBuilder(RestTestClient.Builder<?> clientBuilder) {
 			Assert.state(this.applicationContext != null, "ApplicationContext not injected");
 			getRestTestClientBuilderCustomizers(this.applicationContext)
 				.forEach((customizer) -> customizer.customize(clientBuilder));
@@ -180,10 +170,9 @@ class RestTestClientContextCustomizer implements ContextCustomizer {
 
 		private List<RestTestClientBuilderCustomizer> getRestTestClientBuilderCustomizers(ApplicationContext context) {
 			List<RestTestClientBuilderCustomizer> customizers = new ArrayList<>();
-			SpringFactoriesLoader.forDefaultResourceLocation(context.getClassLoader())
-				.load(RestTestClientBuilderCustomizer.class, ArgumentResolver.of(ApplicationContext.class, context))
-				.forEach(customizers::add);
-			context.getBeansOfType(RestTestClientBuilderCustomizer.class).values().forEach(customizers::add);
+			customizers.addAll(SpringFactoriesLoader.forDefaultResourceLocation(context.getClassLoader())
+				.load(RestTestClientBuilderCustomizer.class, ArgumentResolver.of(ApplicationContext.class, context)));
+			customizers.addAll(context.getBeansOfType(RestTestClientBuilderCustomizer.class).values());
 			return customizers;
 		}
 
diff --git a/integration-test/spring-boot-test-integration-tests/src/test/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizerTests.java b/core/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizerTests.java
similarity index 100%
rename from integration-test/spring-boot-test-integration-tests/src/test/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizerTests.java
rename to core/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactive/client/WebTestClientContextCustomizerTests.java
diff --git a/integration-test/spring-boot-test-integration-tests/src/test/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizerTests.java b/core/spring-boot-test/src/test/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizerTests.java
similarity index 100%
rename from integration-test/spring-boot-test-integration-tests/src/test/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizerTests.java
rename to core/spring-boot-test/src/test/java/org/springframework/boot/test/web/servlet/client/RestTestClientContextCustomizerTests.java