[FIXED] Mocking repository function leads to null pointer exception despite using when and thenReturn

Issue

My ServiceImpl looks like this:

@Service
public class GuildUsersServiceImpl implements GuildUsersService {

  @Autowired
  private final GuildUsersRepository guildUsersRepository;

  @Autowired
  private GuildService guildService;

  @Autowired
  private UserService userService;

  @Autowired
  private GuildUserRoleTypeService guildUserRoleTypeService;

  @Autowired
  public GuildUsersServiceImpl(final GuildUsersRepository guildUsersRepository) {
    this.guildUsersRepository = guildUsersRepository;
  }

  public GuildUsers create(GuildUsers guildUser) {
    return this.guildUsersRepository.save(guildUser);
  }
}

And my service test for create looks like this:

@RunWith(SpringRunner.class)
public class GuildUsersServiceTest {
  
  @Mock private GuildUsersRepository guildUsersRepository;
  
  @Mock private UserService userService;

  @Mock private GuildService guildService;
  
  @Mock private GuildUserRoleTypeService guildUserRoleTypeService;

  @InjectMocks private GuildUsersServiceImpl guildUsersService;
  
  @Before
  public void setUp(){
      MockitoAnnotations.initMocks(this);
  }
  
  @Test
  public void createTest() {
    GuildUsers guildUsers = mockGuildUsers();
    when(guildUsersRepository.save(guildUsers)).thenReturn(guildUsers);
    GuildUsers dbGuildUsers = guildUsersService.create(guildUsers);
    assertEquals(dbGuildUsers.getId(),guildUsers.getId());
  }
}

I am using jUnit4. Despite using when(guildUsersRepository.save(guildUsers)).thenReturn(guildUsers); in the test, I run into a Null Pointer Exception with the following trace:

java.lang.NullPointerException: Cannot invoke "com.project.entities.domain.GuildUsers.getId()" because "dbGuildUsers" is null

I suspect something is wrong with how I have mocked the @Autowired classes. What needs to be done differently while mocking classes in the Test class ?

At the same time I want the services in the following test case to work as well :

@Test
  public void createTest1() {
    GuildUsers guildUsers = mockGuildUsers();
    GuildUsersWithoutGuildIdRequestDTO guildUsersWithoutGuildIdRequestDTO = new  GuildUsersWithoutGuildIdRequestDTO();
    guildUsersWithoutGuildIdRequestDTO.setUserId(guildUsers.getUser().getId());
    guildUsersWithoutGuildIdRequestDTO.setGuildUserRoleTypeId(guildUsers.getGuildUserRoleType().getId());
    
    when(guildService.get(guildUsers.getGuild().getId())).thenReturn(Optional.of(guildUsers.getGuild()));
    when(guildRepository.findById(any())).thenReturn(Optional.of(guildUsers.getGuild()));
    when(userService.get(guildUsers.getUser().getId())).thenReturn(Optional.of(guildUsers.getUser()));
    when(guildUsersRepository.findById(guildUsers.getId())).thenReturn(null);
    when(guildUserRoleTypeService.get(guildUsers.getGuildUserRoleType().getId())).thenReturn(Optional.of(guildUsers.getGuildUserRoleType()));
    when(guildUsersRepository.save(any())).thenReturn(guildUsers);
    
    GuildUsersResponseDTO dbGuildUsersResponseDTO = 
        guildUsersService.create(guildUsers.getGuild().getId(),guildUsersWithoutGuildIdRequestDTO);
    assertEquals(dbGuildUsersResponseDTO.getGuildUserRoleType(),guildUsers.getGuildUserRoleType());
  }

Solution

I don't know why you did field injection as well as constructor injection at the same time. You should remove one of them first, for instance:

@Service
public class GuildUsersServiceImpl implements GuildUsersService {
  
  //@Autowired - removed
  private final GuildUsersRepository guildUsersRepository;

  @Autowired
  private GuildService guildService;

  @Autowired
  private UserService userService;

  @Autowired
  private GuildUserRoleTypeService guildUserRoleTypeService;

  //@Autowired - removed
  public GuildUsersServiceImpl(final GuildUsersRepository guildUsersRepository) {
    this.guildUsersRepository = guildUsersRepository;
  }

  public GuildUsers create(GuildUsers guildUser) {
    return this.guildUsersRepository.save(guildUser);
  }
}

OR remove the constructor to add:

  @Autowired 
  private final GuildUsersRepository guildUsersRepository;```

Answered By - Aman