Why tested class based autowire annotation throw null exception?

Question

I use Spring Boot 5 and JUnit in my project. I create a unit test to test the service.

Here is the service that I am testing:

@Service
@RequiredArgsConstructor
@Slf4j
public class BuilderServiceImpl implements BuilderService{

    @Autowired
    public AutoMapper autoMapper;

    private final BuilderRepository builderRepository;
    private final AdminUserRepository adminUserRepository;


    @Override
    public BuilderDto getByEmail(String email){
    }

    @Override
    public List<BuilderMinDto> getAll() {}

    @Override
    public List<BuilderMinDto> getAll(int page, int size) {}

    @Override
    public SaveBuilderResponse create(Builder builder){

        var str = autoMapper.getDummyText();

        Builder savedBuilder = builderRepository.save(builder);

        return new SaveBuilderResponse(savedBuilder);
    }
}

And here is the test class that tests the service above:

@SpringBootTest
@RequiredArgsConstructor
@Slf4j
class BuilderServiceImplTest {

    @Mock
    private BuilderRepository builderRepository; 
    @Mock
    private AdminUserRepository adminUserRepository; 

    private  AutoCloseable autoCloseable;
    private  BuilderService underTest;

    @BeforeEach
    void setUp(){
        autoCloseable = MockitoAnnotations.openMocks(this);
        underTest = new BuilderServiceImpl(builderRepository,adminUserRepository);
    }

    @AfterEach
    void tearDown () throws Exception{
        autoCloseable.close();
    }

    @Test
    void getByEmail(){}

    @Test
    @Disabled
    void getAll() { }


    @Test
    @Disabled
    void testGetAll() {}

    @Test
    void create() {
        //given
        Builder builder = new Builder();
        builder.setName("John Johnson");
        builder.setCompanyName("Builders Test");
        builder.setEmail("test@builders.com");

        //when
        underTest.create(builder);

        //then
        ArgumentCaptor<Builder> builderArgumentCaptor = ArgumentCaptor.forClass(Builder.class);

        verify(builderRepository)
                .save(builderArgumentCaptor.capture());

        Builder captureBuilder = builderArgumentCaptor.getValue();

        assertThat(captureBuilder).isEqualTo(builder);
    }
}

When I start to run the test class the create method in BuilderServiceImpl fired and on this row:

        var str = autoMapper.getDummyText();
        

I get NullPointerException(autoMapper instance is null).

Here is the definition of AutoMapper class:

@Component
@Slf4j
@RequiredArgsConstructor
public class AutoMapper {

    public String getDummyText(){
        return  "Hello From AutoMapper.";
    }
}

As you can see I use @Component annotation to register the AutoMapper class to the IoC container and Autowired annotation to inject it into autoMapper property in BuilderServiceImpl class.

Why autoMapper instance is null? How can I make autoMapper to be initialized?

Answer 1

Add @Autowire annotation Annotations on below fields. Error due your not initialized below object In BuilderServiceImpl

@Autowire
private final BuilderRepository builderRepository;

@Autowire
private final AdminUserRepository adminUserRepository;

Answer 2

In order to make @Autowire work you have to use the instance of BuilderServiceImpl (object under test) created by spring itself.

When you create the object like this (by yourself, manually):

 @BeforeEach
    void setUp(){
      ....
        underTest = new BuilderServiceImpl(builderRepository,adminUserRepository);
    }

Spring doesn't know anything about this object, hence Autowiring won't work

Another thing that might be useful:

You've used @Mock for BuilderRepository and AdminUserRepository. This are plain mockito annotation, and if you're using an integration/system test that runs the spring under the hood, probably this is not what you want:

Surely, it will create a mock, but it won't put it onto an application context, and won't substitute the beans of these classes that might have been created by spring.

So if this is what you want to achieve, you should use @MockBean instead. This annotation belongs to Spring Testing framework rather than a plain mockito annotation.

All-in-all you might end up with something like this:

@SpringBootTest 
class MyTest
{
   @MockBean
   BuilderRepository builderRepo;
   @MockBean
   AdminUserRepository adminUserRepo;

   @Autowired  // spring will inject your mock repository implementations
               // automatically 
   BuilderServiceImpl underTest;

   @Test
   void mytest() {
      ...
   }
}

Answer 3

Why are you creating BuildService manually? If you do this, set AutoMapper manualy too.

@BeforeEach
    void setUp(){
        autoCloseable = MockitoAnnotations.openMocks(this);
        underTest = new BuilderServiceImpl(builderRepository,adminUserRepository);
        underTest.setAutoMapper(new AutoMapper());
    }

You are not using di.