Test Double :: Mock, Stub and Dummy

UserService.java

public class UserService {
  private final UserDAO userDAO;
  
  public UserService(UserDAO userDAO) {
    this.userDAO = userDAO;
  }
  
  public void createUser(User user) {
    //Some business logic and validation and etc
    userDAO.save(user);
  }
  
}

UserService2.java

public class UserService {
  private final UserDAO userDAO;
  private final UserValidationService userValidationService;
  
  public UserService(UserDAO userDAO, UserValidationService userValidationService) {
    this.userDAO = userDAO;
    this.userValidationService = userValidationService;
  }
  
  public void validate(User user) {
    if(this.userValidationService.isValid(user)) {
      user.setStatus(true);
    } else {
      user.setStatus(false);
    }
  }
  
  public void createUser(User user) {
    //Some business logic and validation and etc
    userDAO.save(user);
  }
  
}

UserServiceTest.java

public class UserServiceTest {
  
  //Test fixtures
  UserDAO userDAO = mock(UserDAO.class);
  UserService userService = new UserService(userDAO);
  User newUser = new User();
  
  @Test
  public void createUser_save_user() {
    //Call method from Class Under Test 
    userService.createUser(newUser);
    
    //Verify expectation
    verify(userDAO).save(newUser);
  }
}

UserServiceTest2.java

public class UserServiceTest {
  
  //Test fixtures
  UserDAO userDAO = mock(UserDAO.class);
  User newUser = new User();
  
  class UserValidationServiceStub extends UserValidationService {
    @Override
    public boolean isValid(User user) {
        return true;
    }
  }
  
  @Test
  public void valid_user_when_validate_is_passed() {
    //Arrange
    UserValidationService userValidationServiceStub = new UserValidationServiceStub();
    UserService userService = new UserService(userDAO, userValidationServiceStub);
  
    //Call method from Class Under Test 
    userService.validate(newUser);
    
    //Verify state
    assertTrue(newUser.isStatus());
  }
}

UserServiceTest3.java

public class UserServiceTest {
  
  //Test fixtures
  User newUser = new User();
  
  class UserDAODummy extends UserDAO {
    public void save(User user) {
      throw new RuntimeException("Not expected to be called");
    }
  }
  
  class UserValidationServiceStub extends UserValidationService {
    @Override
    public boolean isValid(User user) {
        return true;
    }
  }
  
  @Test
  public void valid_user_when_validate_is_passed() {
    //Arrange
    UserDAO userDAODummy = new UserDAODummy();
    UserValidationService userValidationServiceStub = new UserValidationServiceStub();
    UserService userService = new UserService(userDAODummy, userValidationServiceStub);
  
    //Call method from Class Under Test 
    userService.validate(newUser);
    
    //Verify state
    assertTrue(newUser.isStatus());
  }
}