Add auto-configuration for MockMvcTester

This commit adds auto-configuration and documentation for MockMvcTester,
a wrapper of MockMvc that provides AssertJ integration as well as a
fluent API to build requests. The main differences compared to the
regular MockMvc are as follows:

* No need for static imports for building requests and define assertions
* No need to handle unchecked exception as they can be asserted instead
* Support for converting the response body to data types

Closes gh-41198

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/testing/spring-boot-applications.adoc

@@ -140,7 +140,14 @@ include-code::MyApplicationArgumentTests[]
 
 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 {url-spring-framework-docs}/testing/spring-mvc-test-framework.html[`MockMvc`] or `WebTestClient`, as shown in the following example:
+With Spring MVC, we can query our web endpoints using {url-spring-framework-docs}/testing/mockmvc.html[`MockMvc`].
+Three integrations are available:
+
+* The regular {url-spring-framework-docs}/testing/mockmvc/hamcrest.html[`MockMvc`] that uses Hamcrest.
+* {url-spring-framework-docs}/testing/mockmvc/assertj.html[`MockMvcTester`] that wraps `MockMvc` and uses AssertJ.
+* {url-spring-framework-docs}/testing/webtestclient.html[`WebTestClient`] where `MockMvc` is plugged in as the server to handle requests with.
+
+The following example showcases the available integrations:
 
 include-code::MyMockMvcTests[]
 
@@ -345,9 +352,10 @@ Often, `@WebMvcTest` is limited to a single controller and is used in combinatio
 
 `@WebMvcTest` also auto-configures `MockMvc`.
 Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.
+If AssertJ is available, the AssertJ support provided by `MockMvcTester` is auto-configured as well.
 
-TIP: You can also auto-configure `MockMvc` in a non-`@WebMvcTest` (such as `@SpringBootTest`) by annotating it with `@AutoConfigureMockMvc`.
-The following example uses `MockMvc`:
+TIP: You can also auto-configure `MockMvc` and `MockMvcTester` in a non-`@WebMvcTest` (such as `@SpringBootTest`) by annotating it with `@AutoConfigureMockMvc`.
+The following example uses `MockMvcTester`:
 
 include-code::MyControllerTests[]
 
@@ -753,7 +761,13 @@ It can also be used to configure the host, scheme, and port that appears in any
 `@AutoConfigureRestDocs` customizes the `MockMvc` bean to use Spring REST Docs when testing servlet-based web applications.
 You can inject it by using `@Autowired` and use it in your tests as you normally would when using Mock MVC and Spring REST Docs, as shown in the following example:
 
-include-code::MyUserDocumentationTests[]
+include-code::hamcrest/MyUserDocumentationTests[]
+
+If you prefer to use the AssertJ integration, `MockMvcTester` is available as well, as shown in the following example:
+
+include-code::assertj/MyUserDocumentationTests[]
+
+Both reuses the same `MockMvc` instance behind the scenes so any configuration to it applies to both.
 
 If you require more control over Spring REST Docs configuration than offered by the attributes of `@AutoConfigureRestDocs`, you can use a `RestDocsMockMvcConfigurationCustomizer` bean, as shown in the following example:
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/testing/springbootapplications/autoconfiguredspringrestdocs/withmockmvc/assertj/MyUserDocumentationTests.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2024 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.docs.testing.springbootapplications.autoconfiguredspringrestdocs.withmockmvc.assertj;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.assertj.MockMvcTester;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
+
+@WebMvcTest(UserController.class)
+@AutoConfigureRestDocs
+class MyUserDocumentationTests {
+
+	@Autowired
+	private MockMvcTester mvc;
+
+	@Test
+	void listUsers() {
+		assertThat(this.mvc.get().uri("/users").accept(MediaType.TEXT_PLAIN)).hasStatusOk()
+			.apply(document("list-users"));
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/testing/springbootapplications/autoconfiguredspringrestdocs/withmockmvc/assertj/UserController.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.docs.testing.springbootapplications.autoconfiguredspringrestdocs.withmockmvc;
+package org.springframework.boot.docs.testing.springbootapplications.autoconfiguredspringrestdocs.withmockmvc.assertj;
 
 class UserController {
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/testing/springbootapplications/autoconfiguredspringrestdocs/withmockmvc/hamcrest/MyUserDocumentationTests.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.docs.testing.springbootapplications.autoconfiguredspringrestdocs.withmockmvc;
+package org.springframework.boot.docs.testing.springbootapplications.autoconfiguredspringrestdocs.withmockmvc.hamcrest;
 
 import org.junit.jupiter.api.Test;
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/testing/springbootapplications/autoconfiguredspringrestdocs/withmockmvc/hamcrest/UserController.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2012-2024 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.docs.testing.springbootapplications.autoconfiguredspringrestdocs.withmockmvc.hamcrest;
+
+class UserController {
+
+}

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/testing/springbootapplications/springmvctests/MyControllerTests.java

@@ -22,30 +22,28 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
 import org.springframework.boot.test.mock.mockito.MockBean;
 import org.springframework.http.MediaType;
-import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.assertj.MockMvcTester;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
-import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
-import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
-import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(UserVehicleController.class)
 class MyControllerTests {
 
 	@Autowired
-	private MockMvc mvc;
+	private MockMvcTester mvc;
 
 	@MockBean
 	private UserVehicleService userVehicleService;
 
 	@Test
-	void testExample() throws Exception {
+	void testExample() {
 		// @formatter:off
 		given(this.userVehicleService.getVehicleDetails("sboot"))
 			.willReturn(new VehicleDetails("Honda", "Civic"));
-		this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
-			.andExpect(status().isOk())
-			.andExpect(content().string("Honda Civic"));
+		assertThat(this.mvc.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
+			.hasStatusOk()
+			.hasBodyTextEqualTo("Honda Civic");
 		// @formatter:on
 	}
 

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

@@ -23,7 +23,9 @@ import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMock
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.assertj.MockMvcTester;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
@@ -37,6 +39,12 @@ class MyMockMvcTests {
 		mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
 	}
 
+	// If AssertJ is on the classpath, you can use MockMvcTester
+	@Test
+	void testWithMockMvcTester(@Autowired MockMvcTester mvc) {
+		assertThat(mvc.get().uri("/")).hasStatusOk().hasBodyTextEqualTo("Hello World");
+	}
+
 	// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
 	@Test
 	void testWithWebTestClient(@Autowired WebTestClient webClient) {