Configure WebTestClient for @AutoConfigureMockMvc tests

As of Spring Framework 5.3, `WebTestClient` can now be configured on top
of `MockMvc` for testing Spring MVC applications in a mock environment.

Prior to this commit, `WebTestClient` would be already configured for
WebFlux mock setups with `@AutoConfigureWebTestClient` or live servers
(for both MVC and WebFlux apps).

This commit enhances the `@AutoConfigureWebMvc` support so that a
`WebTestClient` instance is auto-configured if the spring-webflux
dependency is present on the classpath.

Closes gh-23067

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

@@ -172,8 +172,9 @@ include::{docs-java}/features/testing/springbootapplications/usingapplicationarg
 
 [[features.testing.spring-boot-applications.with-mock-environment]]
 ==== Testing with a mock environment
-By default, `@SpringBootTest` does not start the server.
-If you have web endpoints that you want to test against this mock environment, you can additionally configure {spring-framework-docs}/testing.html#spring-mvc-test-framework[`MockMvc`] as shown in the following example:
+By default, `@SpringBootTest` does not start the server but instead sets up a mock environment for testing web endpoints.
+
+With Spring MVC, we can query our web endpoints using {spring-framework-docs}/testing.html#spring-mvc-test-framework[`MockMvc`] or `WebTestClient`, as shown in the following example:
 
 [source,java,indent=0,subs="verbatim"]
 ----
@@ -182,7 +183,7 @@ include::{docs-java}/features/testing/springbootapplications/withmockenvironment
 
 TIP: If you want to focus only on the web layer and not start a complete `ApplicationContext`, consider <<features#features.testing.spring-boot-applications.spring-mvc-tests,using `@WebMvcTest` instead>>.
 
-Alternatively, you can configure a {spring-framework-docs}/testing.html#webtestclient-tests[`WebTestClient`] as shown in the following example:
+With Spring WebFlux endpoints, you can use {spring-framework-docs}/testing.html#webtestclient-tests[`WebTestClient`] as shown in the following example:
 
 [source,java,indent=0,subs="verbatim"]
 ----
@@ -214,6 +215,8 @@ For convenience, tests that need to make REST calls to the started server can ad
 include::{docs-java}/features/testing/springbootapplications/withrunningserver/MyRandomPortWebTestClientTests.java[]
 ----
 
+TIP: `WebTestClient` can be used against both live servers and <<features#features.testing.spring-boot-applications.with-mock-environment, mock environments>>.
+
 This setup requires `spring-webflux` on the classpath.
 If you can't or won't add webflux, Spring Boot also provides a `TestRestTemplate` facility:
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/testing/springbootapplications/withmockenvironment/MyMockMvcTests.java

@@ -21,6 +21,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.MockMvc;
 
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
@@ -32,8 +33,20 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 class MyMockMvcTests {
 
 	@Test
-	void exampleTest(@Autowired MockMvc mvc) throws Exception {
+	void testWithMockMvc(@Autowired MockMvc mvc) throws Exception {
 		mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
 	}
 
+	// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
+	@Test
+	void testWithWebTestClient(@Autowired WebTestClient webClient) {
+		// @formatter:off
+		webClient
+				.get().uri("/")
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody(String.class).isEqualTo("Hello World");
+		// @formatter:on
+	}
+
 }

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/servlet/MockMvcAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -19,6 +19,7 @@ package org.springframework.boot.test.autoconfigure.web.servlet;
 import java.util.List;
 
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication.Type;
@@ -28,14 +29,19 @@ import org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguratio
 import org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.test.autoconfigure.web.reactive.WebTestClientAutoConfiguration;
+import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.DispatcherServletCustomizer;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MockMvcBuilder;
+import org.springframework.test.web.servlet.client.MockMvcWebTestClient;
 import org.springframework.test.web.servlet.setup.DefaultMockMvcBuilder;
 import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import org.springframework.web.context.WebApplicationContext;
+import org.springframework.web.reactive.function.client.WebClient;
 import org.springframework.web.servlet.DispatcherServlet;
 
 /**
@@ -44,12 +50,13 @@ import org.springframework.web.servlet.DispatcherServlet;
  * @author Phillip Webb
  * @author Andy Wilkinson
  * @author Stephane Nicoll
+ * @author Brian Clozel
  * @see AutoConfigureWebMvc
  * @since 1.4.0
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnWebApplication(type = Type.SERVLET)
-@AutoConfigureAfter(WebMvcAutoConfiguration.class)
+@AutoConfigureAfter({ WebMvcAutoConfiguration.class, WebTestClientAutoConfiguration.class })
 @EnableConfigurationProperties({ ServerProperties.class, WebMvcProperties.class })
 public class MockMvcAutoConfiguration {
 
@@ -97,6 +104,22 @@ public class MockMvcAutoConfiguration {
 		return mockMvc.getDispatcherServlet();
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnClass({ WebClient.class, WebTestClient.class })
+	static class WebTestClientMockMvcConfiguration {
+
+		@Bean
+		@ConditionalOnMissingBean
+		WebTestClient webTestClient(MockMvc mockMvc, List<WebTestClientBuilderCustomizer> customizers) {
+			WebTestClient.Builder builder = MockMvcWebTestClient.bindTo(mockMvc);
+			for (WebTestClientBuilderCustomizer customizer : customizers) {
+				customizer.customize(builder);
+			}
+			return builder.build();
+		}
+
+	}
+
 	private static class MockMvcDispatcherServletCustomizer implements DispatcherServletCustomizer {
 
 		private final WebMvcProperties webMvcProperties;

spring-boot-project/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -143,7 +143,8 @@ org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2Re
 org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
 org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
 org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
-org.springframework.boot.test.autoconfigure.web.servlet.MockMvcSecurityConfiguration
+org.springframework.boot.test.autoconfigure.web.servlet.MockMvcSecurityConfiguration,\
+org.springframework.boot.test.autoconfigure.web.reactive.WebTestClientAutoConfiguration
 
 # AutoConfigureMockRestServiceServer
 org.springframework.boot.test.autoconfigure.web.client.AutoConfigureMockRestServiceServer=\

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/servlet/MockMvcAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -19,16 +19,26 @@ package org.springframework.boot.test.autoconfigure.web.servlet;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
+import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.web.reactive.function.client.WebClient;
 import org.springframework.web.servlet.DispatcherServlet;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 
 /**
  * Tests for {@link MockMvcAutoConfiguration}.
  *
  * @author Madhura Bhave
+ * @author Brian Clozel
  */
 class MockMvcAutoConfigurationTests {
 
@@ -44,4 +54,35 @@ class MockMvcAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void registersWebTestClient() {
+		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(WebTestClient.class));
+	}
+
+	@Test
+	void shouldNotRegisterWebTestClientIfWebFluxMissing() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader(WebClient.class))
+				.run((context) -> assertThat(context).doesNotHaveBean(WebTestClient.class));
+	}
+
+	@Test
+	void shouldApplyWebTestClientCustomizers() {
+		this.contextRunner.withUserConfiguration(WebTestClientCustomConfig.class).run((context) -> {
+			assertThat(context).hasSingleBean(WebTestClient.class);
+			assertThat(context).hasBean("myWebTestClientCustomizer");
+			verify(context.getBean("myWebTestClientCustomizer", WebTestClientBuilderCustomizer.class))
+					.customize(any(WebTestClient.Builder.class));
+		});
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class WebTestClientCustomConfig {
+
+		@Bean
+		WebTestClientBuilderCustomizer myWebTestClientCustomizer() {
+			return mock(WebTestClientBuilderCustomizer.class);
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/servlet/mockmvc/MockMvcSpringBootTestIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -28,6 +28,7 @@ import org.springframework.boot.test.system.CapturedOutput;
 import org.springframework.boot.test.system.OutputCaptureExtension;
 import org.springframework.context.ApplicationContext;
 import org.springframework.security.test.context.support.WithMockUser;
+import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.MockMvc;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -77,4 +78,9 @@ class MockMvcSpringBootTestIntegrationTests {
 		assertThat(this.applicationContext.getBean(ExampleRealService.class)).isNotNull();
 	}
 
+	@Test
+	void shouldTestWithWebTestClient(@Autowired WebTestClient webTestClient) {
+		webTestClient.get().uri("/one").exchange().expectStatus().isOk().expectBody(String.class).isEqualTo("one");
+	}
+
 }