@MockBean is returning null object

Question

I am trying to use @MockBean; java version 11, Spring Framework Version (5.3.8), Spring Boot Version(2.5.1) and Junit Jupiter (5.7.2) .

    @SpringBootTest
    public class PostEventHandlerTest {
        @MockBean
        private AttachmentService attachmentService;

        @Test
        public void handlePostBeforeCreateTest() throws Exception {
            Post post = new Post("First Post", "Post Added", null, null, "", "");
            
            Mockito.when(attachmentService.storeFile("abc.txt", "")).thenReturn(new Attachment());
     
            PostEventHandler postEventHandler = new PostEventHandler();
            postEventHandler.handlePostBeforeCreate(post);
            verify(attachmentService, times(1)).storeFile("abc.txt", "");
       }
    }

    @Slf4j
    @Component
    @Configuration
    @RepositoryEventHandler
    public class PostEventHandler {
           @Autowired
           private AttachmentService attachmentService;

           @Autowired
           private PostRepository postRepository;

           public void handlePostBeforeCreate(Post post) throws Exception {
             ...
             /* Here attachmentService is found null when we execute above test*/
             attachmentService.storeFile(fileName, content);
             ...
           }
    }

attachmentService is not being mocked it gives null in return

How’s the mocked attachment service suppose to get into your postEventHandler? You have to use Spring‘s mechanisms to create the handler, otherwise it won’t be able to inject mocks at the applicable places. — johanneslink, Aug 09 '21 at 16:41

score 2 · Answer 1 · answered Aug 09 '21 at 05:49

I think you misunderstand the usage of Mocks.

Its true that @MockBean creates a mock (internally uses Mockito) and puts this bean onto an application context so that it will be available for injections, etc.

However, its for your responsibility as a programmer to specify what do you expect from this mock to return when you call one method or another on it.

So, assuming your AttachementService has a method String foo(int):

public interface AttachementService { // or class 
   public String foo(int i);
}

You should specify the expectations with the help of Mockito API:

    @Test
    public void handlePostBeforeCreateTest() throws Exception { 
        // note this line, its crucial
        Mockito.when(attachmentService.foo(123)).thenReturn("Hello");

        Post post = new Post("First Post", "Post Added", null, null, "", "");
        PostEventHandler postEventHandler = new PostEventHandler();
        postEventHandler.handlePostBeforeCreate(post);
        verify(attachmentService, times(1)).storeFile("", null);
   }

If you won't specify the expectation and if your code-under-test calls foo at some point, this method call will return null

Even after adding above line; attachmentService is null inside handlePostBeforeCreate when I run testCase — bhavya, Aug 09 '21 at 10:54
as @bhavya says, your answer does not really help fixing the service being null. — criztovyl, Jul 19 '22 at 19:14
not helping answer at all, seems like he didn't even read the question lol — Drumnbass, Feb 14 '23 at 11:15

score 0 · Answer 2 · edited Jul 18 '22 at 12:09

0

I met a similar problem: I also had null in mocked bean, but only when I run several tests at once (for example, when I run "mvn clean package")

If it was your case (or if it case of someone, who will see this post), then this situation might be solved by annotation @DirtiesContext on every test class youre running

edited Jul 18 '22 at 12:09

Eric Aya

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answered Jul 18 '22 at 09:51

Anton

43
4

score 0 · Answer 3 · answered Jul 19 '22 at 19:54

As @johanneslink said, the problem is this line:

PostEventHandler postEventHandler = new PostEventHandler();

Spring won't inject anything into your PostEventHandler bean if you manually construct it.

The following should make your test work, note the @Autowired postEventHandler. :)

@SpringBootTest
public class PostEventHandlerTest {

    @MockBean
    private AttachmentService attachmentService;

    @Autowired
    PostEventHandler postEventHandler;
    
    @Test
    public void handlePostBeforeCreateTest() throws Exception {
    
        Post post = new Post("First Post", "Post Added", null, null, "", "");
        
        Mockito.when(attachmentService.storeFile("abc.txt", "")).thenReturn(new Attachment());

        postEventHandler.handlePostBeforeCreate(post);
        
        verify(attachmentService, times(1)).storeFile("abc.txt", "");
   }
}

@MockBean is returning null object

3 Answers3