WithMockito.java

public class MainActivityPresenterTestOptionOne implements IMainActivity {

    private static final String SOME_MOCKED_MESSAGE = "Some Mocked Message";
    private Resources resources;
    private MainActivityPresenter mainActivityPresenter;

    @Before
    public void setup(){
        resources = Mockito.mock(Resources.class);
        Mockito.when(resources.getString(R.string.hello_world)).thenReturn(SOME_MOCKED_MESSAGE);

        mainActivityPresenter = new MainActivityPresenter();
        mainActivityPresenter.registerPresenterView(this);
        mainActivityPresenter.setResources(resources);
    }

    @Test
    public void testToastMessage(){
        mainActivityPresenter.fabClicked();
    }

    @Override
    public void showToast(String message) {
        Assert.assertTrue(SOME_MOCKED_MESSAGE.equals(message));
    }
}