Support customization of WebTestClient.Builder when using @SpringBootTest

Closes gh-15132

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -6052,6 +6052,13 @@ include::{code-examples}/test/web/RandomPortTestRestTemplateExampleTests.java[ta
 
 
 
+[[boot-features-testing-spring-boot-applications-customizing-web-test-client]]
+==== Customizing WebTestClient
+To customize the `WebTestClient` bean, configure a `WebTestClientBuilderCustomizer` bean.
+Any such beans are called with the `WebTestClient.Builder` that is used to create the `WebTestClient`.
+
+
+
 [[boot-features-testing-spring-boot-applications-jmx]]
 ==== Using JMX
 As the test context framework caches context, JMX is disabled by default to prevent identical components to register on the same domain.

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/reactive/SpringBootWebTestClientBuilderCustomizer.java

@@ -20,6 +20,7 @@ import java.time.Duration;
 import java.util.Collection;
 import java.util.function.Consumer;
 
+import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer;
 import org.springframework.boot.web.codec.CodecCustomizer;
 import org.springframework.http.codec.ClientCodecConfigurer;
 import org.springframework.test.web.reactive.server.WebTestClient;

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/reactive/WebTestClientAutoConfiguration.java

@@ -28,6 +28,7 @@ import org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration
 import org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer;
 import org.springframework.boot.web.codec.CodecCustomizer;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/reactive/WebTestClientBuilderCustomizer.java

@@ -26,14 +26,12 @@ import org.springframework.test.web.reactive.server.WebTestClient.Builder;
  * @author Andy Wilkinson
  * @since 2.0.0
  * @see WebTestClientAutoConfiguration
+ * @deprecated since 2.2 in favor of
+ * {@link org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer}
  */
 @FunctionalInterface
-public interface WebTestClientBuilderCustomizer {
-
-	/**
-	 * Customize the given {@code builder}.
-	 * @param builder the builder
-	 */
-	void customize(Builder builder);
+@Deprecated
+public interface WebTestClientBuilderCustomizer
+		extends org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer {
 
 }

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/server/WebTestClientBuilderCustomizer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2019 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.boot.test.web.reactive.server;
+
+import org.springframework.test.web.reactive.server.WebTestClient.Builder;
+
+/**
+ * A customizer for a {@link Builder}. Any {@code WebTestClientBuilderCustomizer} beans
+ * found in the application context will be {@link #customize called} to customize the
+ * auto-configured {@link Builder}.
+ *
+ * @author Andy Wilkinson
+ * @since 2.2.0
+ */
+@FunctionalInterface
+public interface WebTestClientBuilderCustomizer {
+
+	/**
+	 * Customize the given {@code builder}.
+	 * @param builder the builder
+	 */
+	void customize(Builder builder);
+
+}

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizer.java

@@ -160,6 +160,7 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 			String port = this.applicationContext.getEnvironment().getProperty("local.server.port", "8080");
 			String baseUrl = (sslEnabled ? "https" : "http") + "://localhost:" + port;
 			WebTestClient.Builder builder = WebTestClient.bindToServer();
+			customizeWebTestClientBuilder(builder, this.applicationContext);
 			customizeWebTestClientCodecs(builder, this.applicationContext);
 			return builder.baseUrl(baseUrl).build();
 		}
@@ -175,6 +176,13 @@ class WebTestClientContextCustomizer implements ContextCustomizer {
 			}
 		}
 
+		private void customizeWebTestClientBuilder(WebTestClient.Builder clientBuilder, ApplicationContext context) {
+			for (WebTestClientBuilderCustomizer customizer : context
+					.getBeansOfType(WebTestClientBuilderCustomizer.class).values()) {
+				customizer.customize(clientBuilder);
+			}
+		}
+
 		private void customizeWebTestClientCodecs(WebTestClient.Builder clientBuilder, ApplicationContext context) {
 			Collection<CodecCustomizer> codecCustomizers = context.getBeansOfType(CodecCustomizer.class).values();
 			if (!CollectionUtils.isEmpty(codecCustomizers)) {

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerIntegrationTests.java

@@ -33,6 +33,11 @@ import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.reactive.server.WebTestClient;
+import org.springframework.test.web.reactive.server.WebTestClient.Builder;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 
 /**
  * Integration test for {@link WebTestClientContextCustomizer}.
@@ -46,8 +51,12 @@ class WebTestClientContextCustomizerIntegrationTests {
 	@Autowired
 	private WebTestClient webTestClient;
 
+	@Autowired
+	private WebTestClientBuilderCustomizer clientBuilderCustomizer;
+
 	@Test
 	void test() {
+		verify(this.clientBuilderCustomizer).customize(any(Builder.class));
 		this.webTestClient.get().uri("/").exchange().expectBody(String.class).isEqualTo("hello");
 	}
 
@@ -60,6 +69,11 @@ class WebTestClientContextCustomizerIntegrationTests {
 			return new TomcatReactiveWebServerFactory(0);
 		}
 
+		@Bean
+		WebTestClientBuilderCustomizer clientBuilderCustomizer() {
+			return mock(WebTestClientBuilderCustomizer.class);
+		}
+
 	}
 
 	static class TestHandler implements HttpHandler {