title: Cannot able to Mock my service's methods in Spring Reactive
body: <p>I am trying to use Spring reactive to develop a chat application. Basically, I have a <strong>CommentRestController</strong> which has <strong>postComment</strong>, and list methods. - I've deleted the list method and some other unnecessary and unrelated methods, since I am not focused on them right now -  Here it is;</p>
  
  <pre><code>@RestController
  @RequiredArgsConstructor
  @RequestMapping("/chat/comment")
  public class CommentRestController {
  
  private final CommentService commentService;
  private final ChannelService channelService;
  
  @PostMapping("/add")
  public Mono&lt;AddCommentResponse&gt; postComment(@Valid @RequestBody Comment comment, ServerWebExchange serverWebExchange) {
      String userName = serverWebExchange.getAttribute("username");
  
      return commentService.save(userName, comment);
  }
  }
  </code></pre>
  
  <p>Now, I am trying to write this Controller's Documentation test. The problem which I've encountered is, I am not able to mock my commentService's <strong>save</strong> method. Its actually mocking the instance but not the method.</p>
  
  <p>Here is my Documentation test class.</p>
  
  <pre><code>@RunWith(SpringRunner.class)
  @SpringBootTest(properties = {"token-validation-service.url = http://localhost:8080/token-validation-service/", "profanity.similarity = 0.9"})
  @AutoConfigureRestDocs(outputDir = "target/generated-snippets")
  public class CommentRestControllerDocumentationTest {
  
  @Rule
  public final JUnitRestDocumentation restDocumentation = new JUnitRestDocumentation();
  
  private WebTestClient webTestClient;
  
  @Autowired
  private CommentRestController commentRestController;
  
  @MockBean
  CommentService commentService;
  
  @MockBean
  ChannelService channelService;
  
  @MockBean
  ServerWebExchange serverWebExchange;
  
  @MockBean
  TokenValidationServiceClient tokenValidationServiceClient;
  
  @MockBean
  OperationResult operationResult;
  
  @MockBean
  AddCommentResponse addCommentResponse;
  
  private RequestHeadersSnippet requestHeaderSnippet = requestHeaders(headerWithName("X-Auth-Token").description("Authentication Access Token"));
  
  private FieldDescriptor responseReturnCode = fieldWithPath("meta.return_code").description("Operation return code");
  private FieldDescriptor responseMessage = fieldWithPath("meta.message").description("Operation message");
  
  private FieldDescriptor idField = fieldWithPath("id").description("id of the comment");
  private FieldDescriptor authorField = fieldWithPath("author").description("Author of the comment");
  private FieldDescriptor commentField = fieldWithPath("text").description("Comment itself");
  private FieldDescriptor channelIdField = fieldWithPath("channelId").description("Channel Id of the comment");
  private FieldDescriptor timestampField = fieldWithPath("timestamp").description("Timestamp of the comment");
  private FieldDescriptor usernameField = fieldWithPath("username").description("Username of the comment, to check who commented");
  private FieldDescriptor isBadField = fieldWithPath("isBad").description("Profanity check for comment");
  
  
  @Before
  public void setUp() {
      webTestClient = WebTestClient.bindToController(commentRestController)
              .configureClient()
              .filter(documentationConfiguration(restDocumentation))
              .build();
  }
  
  @Test
  @WithMockUser
  public void postComment() throws Exception {
  
      String stubName = "postComment";
  
      Comment comment = new Comment();
      comment.setId("1");
      comment.setAuthor("orcun");
      comment.setChannelId("123");
      comment.setText("This is a test method");
      comment.setIsBad(false);
      comment.setTimestamp("1479249799770");
      comment.setUsername("5332109939");
  
      operationResult.setReturnCode(ChatServiceConstants.SUCCESS_CODE);
      operationResult.setMessage(ChatServiceConstants.SUCCESS_MESSAGE);
  
      addCommentResponse.setOperationResult(operationResult);
      when(serverWebExchange.getAttribute("username")).thenReturn("5332109939");
      String userName = serverWebExchange.getAttribute("username");
  
      when(commentService.save(userName, comment)).thenReturn(Mono.just(addCommentResponse));
  
      webTestClient.post().uri("/chat/comment/add")
              .header("X-Auth-Token", "8811-1113")
              .contentType(MediaType.APPLICATION_JSON)
              .accept(MediaType.APPLICATION_JSON)
              .body(BodyInserters.fromObject(comment))
              .exchange()
              .expectStatus().isOk()
              .expectBody()
              .consumeWith(document(stubName,
                      requestFields(idField, authorField, commentField, timestampField,
                              channelIdField, usernameField, isBadField),
                      responseFields(responseReturnCode, responseMessage)));
  }
  }
  </code></pre>
  
  <p>When I run this, I am seeing an error which states response body is empty. Here it is:</p>
  
  <pre><code>org.springframework.restdocs.snippet.SnippetException: Cannot document response fields as the response body is empty
  
  at org.springframework.restdocs.payload.AbstractFieldsSnippet.verifyContent(AbstractFieldsSnippet.java:201)
  at org.springframework.restdocs.payload.AbstractFieldsSnippet.createModel(AbstractFieldsSnippet.java:157)
  at org.springframework.restdocs.snippet.TemplatedSnippet.document(TemplatedSnippet.java:83)
  at org.springframework.restdocs.generate.RestDocumentationGenerator.handle(RestDocumentationGenerator.java:206)
  at org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation.lambda$document$0(WebTestClientRestDocumentation.java:81)
  at org.springframework.test.web.reactive.server.DefaultWebTestClient$DefaultBodyContentSpec.lambda$consumeWith$2(DefaultWebTestClient.java:496)
  at org.springframework.test.web.reactive.server.ExchangeResult.assertWithDiagnostics(ExchangeResult.java:194)
  at org.springframework.test.web.reactive.server.DefaultWebTestClient$DefaultBodyContentSpec.consumeWith(DefaultWebTestClient.java:496)
  at com.turkcell.tvplus.tvpluschat.rest.CommentRestControllerDocumentationTest.postComment(CommentRestControllerDocumentationTest.java:136)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:498)
  at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
  at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
  at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
  at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
  at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:73)
  at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:83)
  at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
  at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
  at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
  at org.springframework.restdocs.JUnitRestDocumentation$1.evaluate(JUnitRestDocumentation.java:63)
  at org.junit.rules.RunRules.evaluate(RunRules.java:20)
  at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
  at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
  at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
  at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
  at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
  at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
  at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
  at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
  at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
  at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
  at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
  at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
  at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
  at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
  at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
  at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
  at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
  at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
  </code></pre>
  
  <p>When I open the path of <strong><em>target/generated-snippets</em></strong>, I am seeing that docs of the method are generated but response-fields.adoc is empty.</p>
  
  <p>I walked over the code with a debug session, and I realized that I am not able to <strong>mock</strong> my <strong><em>commentService.save()</em></strong> method.</p>
  
  <p>Any help will be greatly appreciated.
  Thanks in advance.</p>