TestDemo.kt

@ExperimentalCoroutinesApi
class RestaurantsViewModelTest {
    private val dispatcher = StandardTestDispatcher()
    private val scope = TestScope(dispatcher)

    @Test
    fun stateWithError_isProduced() = scope.runTest {
        val testVM = getViewModel(shouldThrowException = true)
        advanceUntilIdle()
        val currentState = testVM.state.value
        assert(
            currentState == RestaurantsScreenState(
                restaurants = emptyList(),
                isLoading = false,
                error = "error_message"
            )
        )
    }

    private fun getViewModel(shouldThrowException: Boolean = false): RestaurantsViewModel {
        val restaurantsRepository =
            RestaurantsRepository(FakeApiService(shouldThrowException), FakeRoomDao(), dispatcher)
        val getSortedRestaurantsUseCase =
            GetSortedRestaurantsUseCase(restaurantsRepository)
        val getInitialRestaurantsUseCase =
            GetInitialRestaurantsUseCase(
                restaurantsRepository,
                getSortedRestaurantsUseCase
            )
        val toggleRestaurantUseCase = ToggleRestaurantUseCase(
            restaurantsRepository,
            getSortedRestaurantsUseCase
        )
        return RestaurantsViewModel(
            getInitialRestaurantsUseCase,
            toggleRestaurantUseCase,
            dispatcher
        )
    }
}


class FakeApiService(private val shouldThrowException: Boolean) : RestaurantsApiService {
    override suspend fun getRestaurants(): List<RemoteRestaurant> {
        delay(1000)
        if (shouldThrowException)
            throw Exception("error_message")
        return DummyContent.getRemoteRestaurants()
    }

    override suspend fun getRestaurant(id: Int)
            : Map<String, RemoteRestaurant> {
        TODO("Not yet implemented")
    }
}