Android Junit test with mockito

Question

Is my unit test code is correct?

LoginFragmentViewModel.java

private final LoginRepository mLoginRepository;
    MutableLiveData<String> mLoginResponseLiveData;    

    public LoginFragmentViewModel() {
        mLoginRepository = new LoginRepository();
    }

    public LiveData<String> doLogin(String username, String password) {
        mLoginResponseLiveData = mLoginRepository.login(username, password);
        return mLoginResponseLiveData;
    }

LoginFragmentViewModelTest.java

@Test
public void check_do_login(){
        LoginRepository loginRepository = mock(LoginRepository.class);
        MutableLiveData<String> mutableLiveData = mock(MutableLiveData.class);
        mutableLiveData.setValue("Testing value");
        when(loginRepository.login(anyString(), anyString())).thenReturn(mutableLiveData);

        LiveData<String> stringLiveData = mLoginFragmentViewModel.doLogin("username@gmail.com", "password@123");
        assertEquals(stringLiveData.getValue(),"Testing value");
}

Answer 1

You are getting mocking wrong :

MutableLiveData<String> mutableLiveData = mock(MutableLiveData.class);
mutableLiveData.setValue("Testing value");

That first line creates a mock object. This object has nothing to do with the real implementation. Therefore your second call is pointless !

You need a mock specification instead; like for the other mock:

when(mutableLiveData.getValue()).thenReturn("Testing value");

But the question is: are you sure that you have to create a mocked instance of MutableLiveData?

You see - even when you fix that problem I outlined - your test is doing nothing else but "re-implementing" the production code. Yes, the test tests that production code, but as soon as you change your production code, chances are that your test will break.

Long story short:

• consider if you really need to mock mutableLiveData
• maybe your class under test is simply "too small". You want to focus on the public contract of methods for testing; but the contract of your production code is pretty ... small.