How to mock JPA repository's save method in unit tests

Question

For example, I have this method in UserService:

  @Override   @Transactional   public UserDto create(UserDto userDto) {      User dbUser = userRepository.findOne(userDto.getId());      if (dbUser != null) {       throw new AuthException(AuthException.ErrorCode.DUPLICATE_USER_EXCEPTION);     }      User oneByLogin = userRepository.findOneByLogin(userDto.getLogin());     if (oneByLogin != null) {       throw new AuthExceptionAuthException.ErrorCode.DUPLICATE_LOGIN_EXCEPTION);     }      User newUser = new User();     newUser.setGuid(UUID.randomUUID().toString());     newUser.setInsertDate(new Date());     newUser.setFirstName(userDto.getFirstName());     newUser.setLastName(userDto.getLastName());     newUser.setLogin(userDto.getLogin());     newUser.setPassword(userDto.getPassword());     newUser.setAuthToken(TokenGenerator.nextToken());     newUser.setAuthTokenCreatedDate(new Date());      User savedUser = userRepository.save(newUser);      userDto.setAuthToken(savedUser.getAuthToken());     log.info("User {0} created", savedUser.getLogin());     return userDto;   } 

How can I create unit test for this method? I tried next:

  @Test   public void createUser() {      UserDto userDtoRequest = new UserDto();     userDtoRequest.setLogin("Alex");     userDtoRequest.setPassword("123");      UserDto found = userService.create(userDtoRequest);     assertThat(found.getAuthToken()).isNotEmpty(); } 

I have next logic:

1. Test start
2. User dbUser = userRepository.findOne(userDto.getId()); dbUser = NULL
3. if (dbUser != null) and if (oneByLogin != null) skip
4. create new user and set data
5. User savedUser = userRepository.save(newUser); savedUser = NULL

On this step, I have a problem because I cannot mock userRepository.save(newUser).

newUser create inside the method. and test fail. 

savedUser.getAuthToken() - savedUser == NULL

I can rewrite:

    userRepository.save(newUser);     userDto.setAuthToken(newUser.getAuthToken());     log.info("User {0} created", newUser.getLogin());     return userDto; 

but what if I want to use the returned object savedUser?

Answer 1

You need to do this.

when(userRepository.save(Mockito.any(User.class)))                 .thenAnswer(i -> i.getArguments()[0]); 

And now you can obtain user which you pass as argument.