Mockito 然后总是返回 null, Spring-Boot + Junit5 + Z4D1142CA816EAC3E333B383BC0B7B9

Question

I'm trying to implement Mockito to test a particular method but the .thenReturn(...) seems to always be returning a null object instead of what I intended:

User resultUser=userService.save(userDto); The above line return always nullpointer exception.not sure why resultUser always retuning null,

@SpringBootTest
public class UserServiceTests {

@InjectMocks
private UserService userService =new UserServiceImpl();

@Mock
private UserRepository userRepository;

@Mock
BCryptPasswordEncoder passwordEncoder;

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

@DisplayName("Test saveRegistrationTest method making call to Repository")
@Test
public void saveRegistrationTest() {
    
    User user =new User();
    user.setFirstName("TestFN");
    user.setLastName("TestLN");
    user.setEmail("test@test.com");
    user.setPassword("7asdf7asdfi");
    
    User testUser =new User();
    testUser.setFirstName("TestFN");
    
    UserRegistrationDto userDto = new UserRegistrationDto();
    userDto.setFirstName("TestFN");
    
    when(userRepository.save(testUser )).thenReturn(user);
    
    **User resultUser=userService.save(userDto);**
    
    String firstName=(userService.save(userDto)).getFirstName();
    String lastName=(userService.save(userDto)).getLastName();
    String resultEmailFromRepo=(userService.save(userDto)).getEmail();
    String password=(userService.save(userDto)).getPassword();
    
    assertNotNull(user);
    assertEquals("TestLN", firstName);
    assertEquals("TestLN", lastName);
    assertEquals("test@test.com", resultEmailFromRepo);
    assertNotNull(password);
    assertEquals("7asdf7asdfi", password);
}

Answer 1

Don't

@InjectMocks
private UserService userService = new UserServiceImpl();

Just

@SpringBootTest
//...
  @InjectMocks
  private UserService userService; // done!

When we use a concrete object instance as "argument matcher" for mockito:

when(userRepository.save(someObject)).thenReturn(someMock);

, we should ensure, that when (during test):

userRepository(someOtherObject)

..is called,

someObject.equals(someOtherObject)

... is true !("Equality Matcher")

Otherwise mockito can'/won't match that invocation.

We can resolve by, implementing (custom) equals (and hashCode ) methods:

// e.g. with lombok:
@EqualsAndHashCode(onlyExplicitlyIncluded = true)
// ...
class UserRegistrationDto {
  @EqualsAndHashCode.Include
  String name;
}

EqualsAndHashCode (Recommended, but do it well, (lombok small print, or manual!))

---

Or by using a "wider Argument Matcher", like:

when(userRepository.save(any(UserRegistrationDto.class)).thenReturn(myMockResponse);

..or even:

when(userRepository.save(any(/*java.lang.Object*/))...

ArgumentMatchers javadoc