如何用Kotlin Coroutines为Android单元测试注入viewModelScope？

Question

当将CoroutineScope注入到用于单元测试的ViewModel中时，是否也应该使用flowon注入和定义CoroutineDispatcher，即使在生产代码中不需要它？

在此用例中，生产代码中不需要flowon，因为在someRepository.kt中，reverfit处理dispatchers.io上的线程，而viewmodelscope返回dispathers.main上的数据，这两种情况都是默认的。

对保存在Kotlin流值中的Android的ViewModel视图状态值运行单元测试。

主调度程序的模块初始化失败。对于测试，Dispatcher。可以使用kotlinx-coroutines-test模块中的SetMain

在硬编码CoroutineScope的情况下，单元测试在第一次出现时失败。使用viewmodelscope以便启动的coroutine将维护viewmodel的生命周期。但是，viewmodelscope是从ViewModel内部创建的，与可以在ViewModel外部定义并作为参数传入的CoroutineDispatcher相比，这使得注入更加复杂。

SomeViewModel.kt

fun bindIntents(view: FeedView) {
    view.initStateIntent().onEach {
        initState(view)
    }.launchIn(viewModelScope)        
}

Sometest.kt

@ExperimentalCoroutinesApi
class SomeTest : BeforeAllCallback, AfterAllCallback {

    private val testDispatcher = TestCoroutineDispatcher()
    private val testScope = TestCoroutineScope(testDispatcher)
    private val repository = mockkClass(FeedRepository::class)
    private var loadNetworkIntent = MutableStateFlow<LoadNetworkIntent?>(null)

    override fun beforeAll(context: ExtensionContext?) {
        // Set Coroutine Dispatcher.
        Dispatchers.setMain(testDispatcher)
    }

    override fun afterAll(context: ExtensionContext?) {
        Dispatchers.resetMain()
        // Reset Coroutine Dispatcher and Scope.
        testDispatcher.cleanupTestCoroutines()
        testScope.cleanupTestCoroutines()
    }

    @Test
    fun topCafesPoc() = testDispatcher.runBlockingTest {
        coEvery {
            repository.getInitialCafes(any())
        } returns mockGetInitialCafes(mockCafesList, SUCCESS)

        val viewModel = FeedViewModel(repository)
        viewModel.bindIntents(object : FeedView {
            @ExperimentalCoroutinesApi
            override fun initStateIntent() = MutableStateFlow(true)

            @ExperimentalCoroutinesApi
            override fun loadNetworkIntent() = loadNetworkIntent.filterNotNull()

            override fun render(viewState: FeedViewState) {
                // TODO: Test viewState
            }

        })
        loadNetworkIntent.value = LoadNetworkIntent(true)
        // TODO
        // assertEquals(4, 2 + 2)
    }
}

注意：在最终版本中将使用JUnit5测试扩展。

Answer 1

在生产中，由于使用了ViewModel的ViewModelScope，因此使用空的CoroutineScopeProvider创建ViewModel。对于测试，TestCoroutIneScope作为ViewModel参数传递。

Someutils.KT

/**
 * Configure CoroutineScope injection for production and testing.
 *
 * @receiver ViewModel provides viewModelScope for production
 * @param coroutineScope null for production, injects TestCoroutineScope for unit tests
 * @return CoroutineScope to launch coroutines on
 */
fun ViewModel.getViewModelScope(coroutineScope: CoroutineScope?) =
    if (coroutineScope == null) this.viewModelScope
    else coroutineScope

SomeViewModel.kt

class FeedViewModel(
    private val coroutineScopeProvider: CoroutineScope? = null,
    private val repository: FeedRepository
) : ViewModel() {

    private val coroutineScope = getViewModelScope(coroutineScopeProvider)

    fun getSomeData() {
        repository.getSomeDataRequest().onEach {
            // Some code here.            
        }.launchIn(coroutineScope)
    }

}

@ExperimentalCoroutinesApi
class FeedTest : BeforeAllCallback, AfterAllCallback {

    private val testDispatcher = TestCoroutineDispatcher()
    private val testScope = TestCoroutineScope(testDispatcher)
    private val repository = mockkClass(FeedRepository::class)
    private var loadNetworkIntent = MutableStateFlow<LoadNetworkIntent?>(null)

    override fun beforeAll(context: ExtensionContext?) {
        // Set Coroutine Dispatcher.
        Dispatchers.setMain(testDispatcher)
    }

    override fun afterAll(context: ExtensionContext?) {
        Dispatchers.resetMain()
        // Reset Coroutine Dispatcher and Scope.
        testDispatcher.cleanupTestCoroutines()
        testScope.cleanupTestCoroutines()
    }

    @Test
    fun topCafesPoc() = testDispatcher.runBlockingTest {
        ...
        val viewModel = FeedViewModel(testScope, repository)
        viewmodel.getSomeData()
        ...
    }
}