[FIXED] JUnit test. The problem when converting entity to DTO by using ModelMapper library

Issue

I am working on the Spring Boot web app and I have a custom realization of the ModelMapper library that allows me to convert single objects and a list of objects.

@Component
public class ObjectMapperUtils {

@Autowired
private static ModelMapper modelMapper;

static {
    modelMapper = new ModelMapper();
    modelMapper.getConfiguration().setMatchingStrategy(MatchingStrategies.STRICT);
}

private ObjectMapperUtils() {
}

public <D, T> D map(final T entity, Class<D> outClass) {
    return modelMapper.map(entity, outClass);
}

public <D, T> List<D> mapAll(final Collection<T> entityList, Class<D> outCLass) {
    return entityList.stream().map(entity -> map(entity, outCLass)).collect(Collectors.toList());
}
}

On the Service layer, I have a method returns from DB UserEntity object and convert it to UserDTO.

@Autowired
private UserRepository userRepository;

@Autowired
private ObjectMapperUtils modelMapper;

@Override
public UserDTO getByUserId(String userId) {
    UserEntity userEntity = userRepository.findByUserId(userId)
            .orElseThrow(() -> new NotFoundException("User with userId[" + userId + "] not found"));
    //UserDTO userDTO = new UserDTO();
    //BeanUtils.copyProperties(userEntity, userDTO);
    return modelMapper.map(userEntity, UserDTO.class); // userDTO;
}

The problem occurs when I try to create a test for this method. UserDTO always returned as NULL value.

class UserServiceImplTest {

@InjectMocks
private UserServiceImpl userService;

@Mock
private UserRepository userRepository;

@Mock
private ObjectMapperUtils modelMapper;

@BeforeEach
void setUp() throws Exception {
    MockitoAnnotations.initMocks(this);
}

@Test
void testGetByUserId() {
    UserEntity userEntity = new UserEntity();
    userEntity.setId(1L);
    userEntity.setUsername("zavada");
    userEntity.setUserId("33b4c069-e907-45a9-8d49-2042044c56e0");

    when(userRepository.findByUserId(anyString()))
                 .thenReturn(Optional.of(userEntity));

    UserDTO userDTO = userService.getByUserId("33b4c069-e907-45a9-8d49-2042044c56e0");
    System.out.println(userDTO); <--- NULL

    assertEquals("zavada", userDTO.getUsername());
    assertNotNull(userDTO);

}
}

When I use on the Service layer converting by BeanUtils.copyProperties(obj1, obj2); - the test is passed successfully. With ModelMapper I get NULL. Any ideas how to solve this error or refactor code? Thanks in advance

Solution

To build upon user268396 answer you would need the following to get this to work:

@RunWith(MockitoJUnitRunner.class)
    public class StackOverflowTest {

        @InjectMocks
        private StackOverflow userService = new StackOverflow();

        @Mock
        private UserRepository userRepository;

        @Mock
        private ObjectMapperUtils modelMapper;
        private UserDTO userDTO = new UserDTO();
        private UserEntity userEntity = new UserEntity();

        @Before
        public void setUp() {
            when(modelMapper.map(any(), any())).thenReturn(userDTO);

            userDTO.setId(1L);
            userDTO.setUsername("zavada");
            userDTO.setUserId("33b4c069-e907-45a9-8d49-2042044c56e0");
        }

        @Test
        public void testGetByUserId() throws Throwable {
            when(userRepository.findByUserId(anyString())).thenReturn(Optional.of(userEntity));

            UserDTO result = userService.getByUserId("33b4c069-e907-45a9-8d49-2042044c56e0");
            System.out.println(result);

            assertEquals("zavada", result.getUsername());
            assertNotNull(result);

        }
    }

This is quite an easy mistake to make, it is important to remember that all you @mocked objects are not real implementations anymore and if you expect any behaviour back you would need to define it upfront.

Answered By - Slav Pilus