Testing the behavior of void method

Question

Suppose I have the following service object

public class UserService {

    @Autowired
    private UserDao dao;

    public void addUser(String username, String password) {
        if (username.length() < 8 ) {
            username = username  + "random" ; // add some random string
        }
        User user = new User(username, password);

        dao.save(user);
    }
}

I want to test the behaviour of the method "addUser" when username length is less 8 and when the username is more than 8 char. How do approach in unit test UserService.addUser(...), and verify it? I am aware using assert(), but the value "password" is not available outside the addUser(...) method.

I use JUnit and Mockito.

Answer 1

I came up a solution, after some re-visit the problem again after some months.

The idea is to observed the object user that is being passed to UserDao. We can inspect the value of the username by doing this, hence the unit test code:

@RunWith(MockitoJUnitRunner.class)
public class UserServiceTest {
    @Mock
    private UserDao dao;

    @InjectMock
    private UserService service;

    @Test
    public void testAddingUserWithLessThan8CharUsername () {
        final String username = "some";
        final String password = "user";
        doAnswer(new Answer<Object>() {
            @Override
            public Object answer(InvocationOnMock invocationOnMock) throws Throwable {
                Object[] args = invocationOnMock.getArguments();
                User toBeSaved = (User) args[0];
                Assert.assertEquals(username + "random", toBeSaved.getPassword());
                return null;
            }
        }).when(userDao).save(Matchers.any(User.class));
        service.addUser(username, password);
    }
}

Guillaume actually had the closest answer, but he answered using jMock. However, he gave me the idea on how to accomplish this, so I think he deserves some credit too.

Answer 2

You are testing side-effects, but fortunately, everything you need is passed to the dao.save(). First, create a UserDao (either with or without Mockito), then you can use ReflectionTestUtils to set the dao in the UserService, then you can test the values which are passed to dao.save().

Something like:

private class TestUserDao extends UserDao {
    private User savedUser;
    public void save(User user) {
        this.savedUser = user;
    }
}

@Test public void testMethod() {
    UserService userService = new UserService();
    TestUserDao userDao = new TestUserDao();

    ReflectionTestUtils.setField(userService, "dao", userDao);

    userService.addUser("foo", "bar");

    assertEquals("foo", userDao.savedUser.username.substring(0, 3));
    assertEquals("bar", userDao.savedUser.password);
}

Or you can user Mockito to mock out the Dao if you want.