paging.kt

@RunWith(MockitoJUnitRunner::class)
class TvShowViewModelTest {

    private lateinit var viewModel: TvShowViewModel

    @get:Rule
    var instantTaskExecutorRule = InstantTaskExecutorRule()

    @Mock
    private lateinit var catalogueRepository: CatalogueRepository

    @Mock
    private lateinit var observer: Observer<Resource<List<TvShowEntity>>>

    @Mock
    private lateinit var favoredObserver: Observer<PagingData<TvShowEntity>>

    @Before
    fun setUp() {
        viewModel = TvShowViewModel(catalogueRepository)
    }

    @Test
    fun getFavoredTvShows() {
        val dummyTvShows = DataDummy.generateDummyTvShows()
        val data = PagedTestDataSources.snapshot(dummyTvShows)
        val tvShows = MutableLiveData<PagingData<TvShowEntity>>()
        tvShows.value = data

        `when`(catalogueRepository.getFavoredTvShows()).thenReturn(tvShows)
        val tvShowEntities = viewModel.getFavoredTvShows().value
        verify(catalogueRepository).getFavoredTvShows()
        assertNotNull(tvShowEntities)

        viewModel.getFavoredTvShows().observeForever(favoredObserver)
        verify(favoredObserver).onChanged(data)
    }
    
    class PagedTestDataSources private constructor(private val items: List<TvShowEntity>) :
        PagingSource<Int, LiveData<List<TvShowEntity>>>() {
        companion object {
            fun snapshot(items: List<TvShowEntity>): PagingData<TvShowEntity> {
                return PagingData.from(items)
            }
        }

        override fun getRefreshKey(state: PagingState<Int, LiveData<List<TvShowEntity>>>): Int {
            return 0
        }

        override suspend fun load(params: LoadParams<Int>): LoadResult<Int, LiveData<List<TvShowEntity>>> {
            return LoadResult.Page(emptyList(), 0 , 1)
        }
    }
}