使用StateFlow和Coroutines的单元测试StateFlow

Question

Kotlin 1.4.21

我有一个非常简单的ViewModel，它使用coroutine和stateFlow。但是，单元测试将失败，因为stateFlow似乎没有得到更新。

我认为这是因为测试将在stateFlow更新之前完成。

expected not to be empty

这是我的ViewModel正在测试中

class TrendingSearchViewModel @Inject constructor(
    private val loadTrendingSearchUseCase: LoadTrendingSearchUseCase,
    private val coroutineDispatcher: CoroutineDispatcherProvider
) : ViewModel() {

    private val trendingSearchMutableStateFlow = MutableStateFlow<List<String>>(emptyList())
    val trendingSearchStateFlow = trendingSearchMutableStateFlow.asStateFlow()

    fun getTrendingSearch() {
        viewModelScope.launch(coroutineDispatcher.io()) {
            try {
                trendingSearchMutableStateFlow.value = loadTrendingSearchUseCase.execute()
            } catch (exception: Exception) {
                Timber.e(exception, "trending ${exception.localizedMessage}")
            }
        }
    }
}

这是我的真正的考试课，我试过不同的方法让它开始工作。

class TrendingSearchViewModelTest {
    private val loadTrendingSearchUseCase: LoadTrendingSearchUseCase = mock()
    private val coroutineDispatcherProvider = CoroutineDispatcherProviderImp()
    private lateinit var trendingSearchViewModel: TrendingSearchViewModel

    @Before
    fun setUp() {
        trendingSearchViewModel = TrendingSearchViewModel(
            loadTrendingSearchUseCase,
            coroutineDispatcherProvider
        )
    }

    @Test
    fun `should get trending search suggestions`() {
        runBlocking {
            // Arrange
            val trending1 = UUID.randomUUID().toString()
            val trending2 = UUID.randomUUID().toString()
            val trending3 = UUID.randomUUID().toString()

            whenever(loadTrendingSearchUseCase.execute()).thenReturn(listOf(trending1, trending2, trending3))

            val job = launch {
                trendingSearchViewModel.trendingSearchStateFlow.value
            }

            // Act
            trendingSearchViewModel.getTrendingSearch()

            // Assert
            val result = trendingSearchViewModel.trendingSearchStateFlow.value
            assertThat(result).isNotEmpty()

            job.cancel()
        }
    }
}

这是我在测试中嘲笑的用法：

class LoadTrendingSearchUseCaseImp @Inject constructor(
    private val searchCriteriaProvider: SearchCriteriaProvider,
    private val coroutineDispatcherProvider: CoroutineDispatcherProvider
) : LoadTrendingSearchUseCase {

    override suspend fun execute(): List<String> {
        return withContext(coroutineDispatcherProvider.io()) {
            searchCriteriaProvider.provideTrendingSearch().trendingSearches
        }
    }
}

万一需要的话，这就是我的界面：

interface CoroutineDispatcherProvider {
    fun io(): CoroutineDispatcher = Dispatchers.IO
    fun default(): CoroutineDispatcher = Dispatchers.Default
    fun main(): CoroutineDispatcher = Dispatchers.Main
    fun immediate(): CoroutineDispatcher = Dispatchers.Main.immediate
    fun unconfined(): CoroutineDispatcher = Dispatchers.Unconfined
}

class CoroutineDispatcherProviderImp @Inject constructor() : CoroutineDispatcherProvider

Answer 1

这就是对我有用的东西：

@Test
fun `should get trending search suggestions`() {
    runBlockingTest {
        // Arrange
        val trending1 = UUID.randomUUID().toString()
        val trending2 = UUID.randomUUID().toString()
        val trending3 = UUID.randomUUID().toString()
        val listOfTrending = listOf(trending1, trending2, trending3)

        whenever(loadTrendingSearchUseCase.execute()).thenReturn(listOfTrending)

        /* List to collect the results */
        val listOfEmittedResult = mutableListOf<List<String>>()
        val job = launch {
            trendingSearchViewModel.trendingSearchStateFlow.toList(listOfEmittedResult)
        }

        // Act
        trendingSearchViewModel.getTrendingSearch()

        // Assert
        assertThat(listOfEmittedResult).isNotEmpty()
        verify(loadTrendingSearchUseCase).execute()

        job.cancel()
    }
}

Answer 2

我认为，当您需要更复杂的场景时，这个由杰克·沃顿( Jack )编写的库https://github.com/cashapp/turbine将会有很大的帮助。

我认为正在发生的是，在片段中调用.collect { }，这确保了流的启动。检查终端操作符定义:流上的终端操作符是挂起启动流的集合的函数。https://kotlinlang.org/docs/flow.html#terminal-flow-operators

对于sharedFlow来说则不是这样，它可能被配置为急切地启动。

所以为了解决你的问题，你可以打电话给

val job = launch {
    trendingSearchViewModel.trendingSearchStateFlow.collect()
}