marcinOz

class MovieListViewModel @Inject constructor(private val dataProvider: DataProvider) : ViewModel() {

  val movieDiscover = MutableLiveData<List<Movie>>()

  fun fetchMovieDiscover() {
    dataProvider.getMovieDiscover().subscribeBy(
      onSuccess = { result ->  movieDiscover.postValue(result)
      },
      onError = { error -> movieDiscover.postValue(null) }
    )

marcinOz

sealed class ResourceState

class LoadingState : ResourceState()
class EmptyState : ResourceState()
data class PopulatedState<T>(val data: T) : ResourceState()
data class ErrorState(val message: String?) : ResourceState()

marcinOz

class MovieListViewModel @Inject constructor(private val dataProvider: DataProvider) : ViewModel() {

  val movieDiscover = MutableLiveData<ResourceState>()

  fun fetchMovieDiscover() {
    movieDiscover.postValue(LoadingState())
    dataProvider.getMovieDiscover().subscribeBy(
      onSuccess = { result ->
        if (result.isEmpty()) movieDiscover.postValue(EmptyState())
        else movieDiscover.postValue(PopulatedState(result))

marcinOz

movieDiscover.observe(activity, Observer { it?.apply { updateView(this) }})

private fun updateView(resourceState: ResourceState) = when(resourceState) {
  is LoadingState -> showLoading(true)
  is PopulatedState<*> -> populate(resourceState.data as List<Movie>)
  is EmptyState -> showEmptyMessage() 
  is ErrorState -> showError(resourceState.message)
}

marcinOz

sealed class ResourceState<T>

class LoadingState<T> : ResourceState<T>()
class EmptyState<T> : ResourceState<T>()
data class PopulatedState<T>(val data: T) : ResourceState<T>()
data class ErrorState<T>(val message: String?) : ResourceState<T>()

marcinOz

//MovieListViewModel
val movieDiscover = MutableLiveData<ResourceState<List<Movie>>>()

//View
private fun updateView(resourceState: ResourceState<List<Movie>>) = when(resourceState) {
    is LoadingState -> showLoading(true)
    is PopulatedState -> populate(resourceState.data)
    is EmptyState -> showEmptyMessage()
    is ErrorState -> showError(resourceState.message)
  }

marcinOz

 @Rule
 @JvmField
 val instantExecutorRule = InstantTaskExecutorRule() //Very very important

marcinOz

  @Mock
  private lateinit var dataProvider: DataProvider
  @Mock lateinit var observer: Observer<ResourceState<List<Movie>>>
  private lateinit var viewModel: MovieListViewModel

  @Before
  fun init() {
    MockitoAnnotations.initMocks(this)
    viewModel = MovieListViewModel(dataProvider)
      .apply { movieDiscover.observeForever(observer) }

marcinOz

  private fun mockFetchMovieDiscover(block: SingleEmitter<MovieDiscoveryResponse>.() -> Unit) {
    `when`(dataProvider.getMovieDiscover()).thenReturn(Single.create { e -> e.block() })
  }
  
  @Test
  fun fetchMovieDiscover_test_success_with_empty() {
    mockFetchMovieDiscover { onSuccess(emptyList()) }

    viewModel.fetchMovieDiscover()

marcinOz

sealed class ResourceState<T>

class LoadingState<T> : ResourceState<T>() {
  override fun hashCode(): Int = javaClass.hashCode()
  override fun equals(other: Any?) = equalz(other)
}
class EmptyState<T> : ResourceState<T>() {
  override fun hashCode(): Int = javaClass.hashCode()
  override fun equals(other: Any?) = equalz(other)
}