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

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());
  }

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;```

</details>



# 答案2
**得分**: 0

InjectMock文档明确表示：“Mockito只会尝试通过构造函数注入、setter注入或按顺序和如下所述的属性注入来注入模拟。”

在您的情况下，显然它选择了属性注入，因此guildUserRoleTypeService保持未初始化状态。正如上面指出的，混合使用属性注入和构造函数注入并不是一个好主意。

为了改进GuildUsersServiceImpl的总体设计和可测试性，我建议坚持使用构造函数注入。这样您可以：
a）将所有字段声明为private final，这样一旦对象创建，它们就会被设置，避免了竞态条件和空指针异常。
b）在测试中使用适当的构造函数初始化GuildUsersServiceImpl，而不是使用InjectMocks。

<details>
<summary>英文:</summary>

InjectMock documentation clearly says: &quot;Mockito will try to inject mocks only either by constructor injection, setter injection, or property injection in order and as described below.&quot;

In your case, it apparently chooses property injection, hence guildUserRoleTypeService remains uninitialised. Mixing property and constructor injection is not a good idea as pointed above.

To improve the general design and testability of your GuildUsersServiceImpl, I would suggest to stick with constructor injection. This way you can:
a) Declare all the fields as private final, so they will always be set once the object is created, avoiding race conditions and NPEs.
b) Initialise GuildUsersServiceImpl in the test using a proper constructor rather than InjectMocks.



</details>



# 答案3
**得分**: 0

把这个留在这里，为了其他也在浪费一个下午尝试让存储库返回他们配置的内容的人。最终我需要做的是，与其用`@Mock`注解存储库，我必须使用`@MockBean`注解，以使Mockito/Spring组合正常工作。

根据`@MockBean`的javadoc：

&gt; 当在字段上使用@MockBean时，除了在应用程序上下文中注册外，该模拟还将被注入到该字段中。

<details>
<summary>英文:</summary>

Leaving this here for other people that also wasted an afternoon on trying to get a repository to return what they configured. What ended up being the thing I had to do is rather than annotating the repository with `@Mock` I had to use the `@MockBean` annotation for the Mockito/Spring combination to work properly.

As per javadoc of `@MockBean`:

&gt; When @MockBean is used on a field, as well as being registered in the application context, the mock will also be injected into the field.

</details>