Unit Testing MVP using mockito with event listeners

Question

Android Studio 2.1.2

I want to test that the callbacks onUsernameError, onPasswordError, and onSuccess, in the LoginModelImp are actually called. I am not sure how to test event listeners. However, the test fails as those functions are never called. I am mocking them with mockito and trying to verify them.

This is my code so far.

Presenter interface

public interface LoginPresenterContract<LoginFragmentViewContract> {
    void validateCredentials();

    void attachView(LoginFragmentViewContract view);
    void detachView();
}

Presenter implementation

public class LoginPresenterImp implements LoginPresenterContract<LoginFragmentViewContract>, LoginModelContract.OnLoginCompletedListener {

    private LoginModelContract mLoginModelContract;
    private LoginFragmentViewContract mLoginFragmentView;

    public LoginPresenterImp(LoginModelContract loginModelContract) {
        mLoginModelContract = loginModelContract;
    }

    /*
     * LoginPresenterContact - implementation
     */
    @Override
    public void attachView(LoginFragmentViewContract view) {
        mLoginFragmentView = view;
    }

    @Override
    public void detachView() {
        mLoginFragmentView = null;
    }

    @Override
    public void validateCredentials() {
        if(mLoginModelContract != null) {
            mLoginModelContract.login(
                    mLoginFragmentView.getUsername(),
                    mLoginFragmentView.getPassword(),
                    LoginPresenterImp.this);
        }
    }

    /*
     * LoginModelContract.OnLoginCompletedListener - implementation
     */
    @Override
    public void onUsernameError() {
        if(mLoginFragmentView != null) {
            mLoginFragmentView.onLoginFailed("Incorrect username");
        }
    }

    @Override
    public void onPasswordError() {
        if(mLoginFragmentView != null) {
            mLoginFragmentView.onLoginFailed("Incorrect password");
        }
    }

    @Override
    public void onSuccess() {
        if(mLoginFragmentView != null) {
            mLoginFragmentView.onLoginSuccess();
        }
    }
}

Model interface

public interface LoginModelContract {
    interface OnLoginCompletedListener {
        void onUsernameError();
        void onPasswordError();
        void onSuccess();
    }
    void login(String username, String password, OnLoginCompletedListener onLoginCompletedListener);
}

Model Implementation

public class LoginModelImp implements LoginModelContract {
    /* Testing Valid username and passwords */
    private static String validUsername = "steve";
    private static String validPassword = "1234";

    @Override
    public void login(final String username,
                      final String password,
                      final OnLoginCompletedListener onLoginCompletedListener) {

        boolean hasSuccess = true;
        if(TextUtils.isEmpty(username) || !username.equals(validUsername)) {
        /* TEST onUsernameError() */
            onLoginCompletedListener.onUsernameError();
            hasSuccess = false;
        }

        if(TextUtils.isEmpty(password) || !password.equals(validPassword)) {
        /* TEST onPasswordError() */
            onLoginCompletedListener.onPasswordError();
            hasSuccess = false;
        }

        if(hasSuccess) {
        /* TEST onSuccess() */
            onLoginCompletedListener.onSuccess();
        }
    }
}

JUnit4 test with Mockito

public class LoginPresenterImpTest {
    private LoginFragmentViewContract mMockViewContract;
    private LoginModelContract mMockModelContract;
    private LoginModelContract.OnLoginCompletedListener mMockOnLoginCompletedListener;
    private LoginPresenterContract<LoginFragmentViewContract> mLoginPresenterContract;

    @Before
    public void setUp() throws Exception {
        mMockViewContract = Mockito.mock(LoginFragmentViewContract.class);
        mMockModelContract = Mockito.mock(LoginModelContract.class);
        mMockOnLoginCompletedListener = Mockito.mock(LoginModelContract.OnLoginCompletedListener.class);
        mLoginPresenterContract = new LoginPresenterImp(mMockModelContract);
        mLoginPresenterContract.attachView(mMockViewContract);
    }

    @Test
    public void shouldSuccessWithValidCredentials() {
        when(mMockViewContract.getUsername()).thenReturn("steve");
        when(mMockViewContract.getPassword()).thenReturn("1234");

        mLoginPresenterContract.validateCredentials();

        verify(mMockViewContract, times(1)).getUsername();
        verify(mMockViewContract, times(1)).getPassword();

        verify(mMockOnLoginCompletedListener, times(1)).onSuccess();

        verify(mMockOnLoginCompletedListener, never()).onPasswordError();
        verify(mMockOnLoginCompletedListener, never()).onUsernameError();
    }
}

Is there any way to test this implementation?

Many thanks for any suggestions,

Answer 1

The test class LoginPresenterImpTest is about the test of LoginPresenterImp class, and it should use only its actual implementation and the mocks of its collaborators. The class LoginModelContract.OnLoginCompletedListener is a collaborator of LoginModelImp, so in a well designed, and pure unit-test of LoginPresenterImp, like yours, it's perfectly normal that it is never called. The solution I propose is to test the LoginModelImp separately:

public class LoginModelImpTest {

    private LoginModelContract.OnLoginCompletedListener mMockOnLoginCompletedListener;
    private LoginModelImp loginModelImp;

    @Before
    public void setUp() throws Exception {
        mMockOnLoginCompletedListener = Mockito.mock(LoginModelContract.OnLoginCompletedListener.class);
        loginModelImp = new LoginModelImp();
    }

    @Test
    public void shouldSuccessWithValidCredentials() {

        loginModelImp.login("steve", "1234", mMockOnLoginCompletedListener);;

        verify(mMockOnLoginCompletedListener, times(1)).onSuccess();

        verify(mMockOnLoginCompletedListener, never()).onPasswordError();
        verify(mMockOnLoginCompletedListener, never()).onUsernameError();
    }
}

Alternatively, you have to use the actual implementation of LoginModelImp in your LoginPresenterImpTest and spy on your listener (that is the presenter itself) or to configure the mocks to make them call the listener. Here's an example, but I wouldn't use this one:

public class LoginPresenterImpTest {
    private LoginFragmentViewContract mMockViewContract;
    private LoginModelContract mModelContract;
    private LoginModelContract.OnLoginCompletedListener mMockOnLoginCompletedListener;
    private LoginPresenterContract<LoginFragmentViewContract> mLoginPresenterContract;

    @Before
    public void setUp() throws Exception {
        mMockViewContract = Mockito.mock(LoginFragmentViewContract.class);
        mModelContract = new LoginModelImp();
        LoginPresenterImp spyPresenterImp = Mockito.spy(new LoginPresenterImp(mModelContract));
        mLoginPresenterContract = spyPresenterImp;
        mMockOnLoginCompletedListener = spyPresenterImp;
        mLoginPresenterContract.attachView(mMockViewContract);
    }

    @Test
    public void shouldSuccessWithValidCredentials() {
        when(mMockViewContract.getUsername()).thenReturn("steve");
        when(mMockViewContract.getPassword()).thenReturn("1234");

        mLoginPresenterContract.validateCredentials();

        verify(mMockViewContract, times(1)).getUsername();
        verify(mMockViewContract, times(1)).getPassword();

        verify(mMockOnLoginCompletedListener, times(1)).onSuccess();

        verify(mMockOnLoginCompletedListener, never()).onPasswordError();
        verify(mMockOnLoginCompletedListener, never()).onUsernameError();
    }
}