ResponseEntity is always null in Mockito while calling function from a service class

Question

I have created a service class

@Service
public class SomeServiceImpl implements SomeService {
    @Override
    public ResponseEntity<?> getMethod() {
        EntityClass entity = new EntityClass();
        //Some operations to manipulate entity
        return new ResponseEntity<>("entity", HttpStatus.OK);
    }
}

I'm trying to get the object in a test class using Mockito:

@AutoConfigureMockMvc
@RunWith(MockitoJUnitRunner.class)
@Slf4j
public class SomeServiceTest {
    @Mock
    SomeService someService;
    @Test
    public void getMethodSomeService(){
        ResponseEntity<?> responseEntity=someService.getMethod();
        log.debug("{}", responseEntity);
    }
}

However, responseEntity is always null . What am I doing wrong? Am I missing something? Why the value I got is always null?

Answer 1

By writing

@Mock
SomeService someService;

You have created a mock, all method calls to that mock will return null unless you tell it to do otherwise with something like this

when(someService.someMethod(any())).thenReturn("something");

Because of this someService.getMethod() will always return null. You are probably looking to not use a mock in this case, mocks are usually used to prevent calls to other objects that aren't supposed to be part of the unit test.

Answer 2

Mocking means replacing a concrete implementation with something you can manipulate from the outside. If you want to test your SomeServiceImpl , you can just create a new instance.

SomeService service = new SomeServiceImpl();

This instance can then be tested.

---

If your SomeService had a dependency to let's say another Service, you might need to mock this dependency in order to control its behaviour.

@Mock
OtherService dependency;
SomeService someService = new SomeServiceImpl(dependency);