Как смоделировать репозитарий liveata и методы ViewModel для модульного тестирования

Question

Как правильно проверить проверку viewModel.getMoviesByReleaseDate() получает List<DiscoverMovie> при вызове repository.getMoviesByReleaseDate() на viewModel.init().

Мой метод testRepoFetchDataSuccess() не достигает вышеупомянутого. Пожалуйста, приведите пример кода, если это возможно, поскольку я новичок в модульном тестировании.

public class TMDbRepository {

    private static final String TAG = "TMDbRepository";

    private static final String RELEASE_DATE_LTE = "2020-02-02";
    private static final String RELEASE_DATE_DESC = "release_date.desc";
    private static final int PAGES_NO = 1;

    private final TMDbWebService webService;

    @Inject
    public TMDbRepository(TMDbWebService webService) {
        this.webService = webService;
    }

    public Single<DiscoverMovieResponse> getMoviesByReleaseDate() {
        return webService
                .getMoviesByReleaseDate(RELEASE_DATE_LTE, RELEASE_DATE_DESC, PAGES_NO);
    }

    public Single<MovieDetails> getMovieDetails(int id) {
        return webService.getMovieDetails(id);
    }
}

public class MasterFragmentViewModel extends ViewModel {
    private static final String TAG = "MasterFragmentViewModel";

    private final RxSingleSchedulers rxSingleSchedulers;
    private final TMDbRepository repository;
    private CompositeDisposable disposable;

    private final MutableLiveData<List<DiscoverMovie>> movies = new MutableLiveData<>();
    private final MutableLiveData<Boolean> error = new MutableLiveData<>();
    private final MutableLiveData<Boolean> loading = new MutableLiveData<>();

    @Inject
    public MasterFragmentViewModel(TMDbRepository repository, RxSingleSchedulers rxSingleSchedulers) {
        this.repository = repository;
        this.rxSingleSchedulers = rxSingleSchedulers;
        disposable = new CompositeDisposable();
    }

    public void init() {
        fetchMoviesByReleaseDate();
    }

    private void fetchMoviesByReleaseDate() {
        loading.setValue(true);

        disposable.add(
                repository.getMoviesByReleaseDate()
                        .compose(rxSingleSchedulers.applySchedulers())
                        .subscribeWith(new DisposableSingleObserver<DiscoverMovieResponse>() {
                            @Override
                            public void onSuccess(DiscoverMovieResponse discoverMovieResponse) {
                                error.setValue(false);
                                movies.setValue(discoverMovieResponse.getMovieList());
                                loading.setValue(false);
//                                Log.d(TAG, "onSuccess: " + discoverMovieResponse.getTotalResults());
                            }

                            @Override
                            public void onError(Throwable e) {
                                Log.d(TAG, "onError: " + e);
                                error.setValue(true);
                                loading.setValue(false);
                            }
                        })
        );
    }

    public LiveData<List<DiscoverMovie>> getMoviesByReleaseDate() {
        return movies;
    }

    public LiveData<Boolean> getError() {
        return error;
    }

    public LiveData<Boolean> getLoading() {
        return loading;
    }

    @Override
    protected void onCleared() {
        super.onCleared();
        disposable.clear();
        Log.d(TAG, "onCleared: disposable cleared!");
    }
}

public class MasterFragmentTest {

    @Rule
    public InstantTaskExecutorRule instantExecutorRule = new InstantTaskExecutorRule();
    @Mock
    TMDbRepository repository;
    @Mock
    LifecycleOwner lifecycleOwner;
    @Mock
    Observer<List<DiscoverMovie>> moviesObserver;
    Lifecycle lifecycle;
    private MasterFragmentViewModel viewModel;

    @Before
    public void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
        lifecycle = new LifecycleRegistry(lifecycleOwner);
        viewModel = new MasterFragmentViewModel(repository, RxSingleSchedulers.TEST_SCHEDULER);
        viewModel.getMoviesByReleaseDate().observeForever(moviesObserver);
    }

    @Test
    public void testNull() {
        when(repository.getMoviesByReleaseDate()).thenReturn(null);
        assertNotNull(viewModel.getMoviesByReleaseDate());
        assertTrue(viewModel.getMoviesByReleaseDate().hasObservers());
    }

    @Test
    public void testRepoFetchDataSuccess() {
        List<DiscoverMovie> mockList = new ArrayList<>();
        DiscoverMovie discoverMovie = Mockito.mock(DiscoverMovie.class);
        mockList.add(discoverMovie);

        when(repository.getMoviesByReleaseDate()).thenReturn(Single.just(new DiscoverMovieResponse()));
        viewModel.init();
        verify(moviesObserver).onChanged(mockList);
    }

    @After
    public void tearDown() throws Exception {
        repository = null;
        viewModel = null;
    }
}

Результат теста:

Argument(s) are different! Wanted:
moviesObserver.onChanged(
    [Mock for DiscoverMovie, hashCode: 990897274]
);
-> at com.sulaz.tmdb.MasterViewModelTest.testRepoFetchDataSuccess(MasterViewModelTest.java:72)
Actual invocation has different arguments:
moviesObserver.onChanged(
    null
);
-> at androidx.lifecycle.LiveData.considerNotify(LiveData.java:131)