在 Kotlin 中测试 CoroutineScope 基础设施

Question

有人能告诉我如何使这个 viewModel 中的 getMovies 函数可测试吗？我无法让单元测试正确地等待协程..

(1) 我很确定我必须创建一个 test-CoroutineScope 和一个正常的 lifeCycle-CoroutineScope，如 this Medium Article 所示。

(2) 一旦定义了范围，我也不确定如何告诉 getMovies() 在给定普通应用上下文或测试上下文的情况下它应该使用哪个范围。

enum class MovieApiStatus { LOADING, ERROR, DONE }

class MovieListViewModel : ViewModel() {

    var pageCount = 1


    private val _status = MutableLiveData<MovieApiStatus>()
    val status: LiveData<MovieApiStatus>
        get() = _status    
    private val _movieList = MutableLiveData<List<Movie>>()
    val movieList: LiveData<List<Movie>>
        get() = _movieList    

    // allows easy update of the value of the MutableLiveData
    private var viewModelJob = Job()

    // the Coroutine runs using the Main (UI) dispatcher
    private val coroutineScope = CoroutineScope(
        viewModelJob + Dispatchers.Main
    )

    init {
        Log.d("list", "in init")
        getMovies(pageCount)
    }

    fun getMovies(pageNumber: Int) {

        coroutineScope.launch {
            val getMoviesDeferred =
                MovieApi.retrofitService.getMoviesAsync(page = pageNumber)
            try {
                _status.value = MovieApiStatus.LOADING
                val responseObject = getMoviesDeferred.await()
                _status.value = MovieApiStatus.DONE
               ............

            } catch (e: Exception) {
                _status.value = MovieApiStatus.ERROR
                ................
            }
        }
        pageCount = pageNumber.inc()
    }
...
}

它使用这个 API 服务...

package com.example.themovieapp.network

import com.jakewharton.retrofit2.adapter.kotlin.coroutines.CoroutineCallAdapterFactory
import com.squareup.moshi.Moshi
import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
import kotlinx.coroutines.Deferred
import retrofit2.Retrofit
import retrofit2.converter.moshi.MoshiConverterFactory
import retrofit2.http.GET
import retrofit2.http.Query

private const val BASE_URL = "https://api.themoviedb.org/3/"
private const val API_key  = ""

private val moshi = Moshi.Builder()
    .add(KotlinJsonAdapterFactory())
    .build()

private val retrofit = Retrofit.Builder()
    .addConverterFactory(MoshiConverterFactory.create(moshi))
    .addCallAdapterFactory(CoroutineCallAdapterFactory())
    .baseUrl(BASE_URL)
    .build()


interface MovieApiService{
//https://developers.themoviedb.org/3/movies/get-top-rated-movies
//https://square.github.io/retrofit/2.x/retrofit/index.html?retrofit2/http/Query.html
    @GET("movie/top_rated")
    fun getMoviesAsync(
        @Query("api_key") apiKey: String = API_key,
        @Query("language") language: String = "en-US",
        @Query("page") page: Int
    ): Deferred<ResponseObject>
}


/*
Because this call is expensive, and the app only needs
one Retrofit service instance, you expose the service to the rest of the app using
a public object called MovieApi, and lazily initialize the Retrofit service there
*/
object MovieApi {
    val retrofitService: MovieApiService by lazy {
        retrofit.create(MovieApiService::class.java)
    }
}

我只是想创建一个测试，在函数之后断言 liveData“状态”为 DONE。

这里是Project Repository

Answer 1

首先，您需要以某种方式使您的协程作用域可注入，或者通过手动为其创建提供程序，或者使用像 dagger 这样的注入框架。这样，当您测试 ViewModel 时，您可以使用测试版本覆盖协程范围。

有几个选择可以做到这一点，您可以简单地使 ViewModel 本身可注入（此处的文章：https://medium.com/chili-labs/android-viewmodel-injection-with-dagger-f0061d3402ff）

或者您可以手动创建一个 ViewModel 提供程序并在创建它的任何地方使用它。无论如何，我强烈建议使用某种形式的依赖注入以实现真正的可测试性。

无论如何，您的 ViewModel 需要 提供其 CoroutineScope，而不是实例化协程范围本身。

换句话说，你可能想要

class MovieListViewModel(val couroutineScope: YourCoroutineScope) : ViewModel() {}

或许

class MovieListViewModel @Inject constructor(val coroutineScope: YourCoroutineScope) : ViewModel() {}

无论您为注入做什么，下一步都是创建您自己的 CoroutineScope 接口，您可以在测试上下文中覆盖该接口。例如：

interface YourCoroutineScope : CoroutineScope {
    fun launch(block: suspend CoroutineScope.() -> Unit): Job
}

这样，当你为你的应用使用作用域时，你可以使用一个作用域，比如说，生命周期协程作用域：

class LifecycleManagedCoroutineScope(
        private val lifecycleCoroutineScope: LifecycleCoroutineScope,
        override val coroutineContext: CoroutineContext = lifecycleCoroutineScope.coroutineContext) : YourCoroutineScope {
    override fun launch(block: suspend CoroutineScope.() -> Unit): Job = lifecycleCoroutineScope.launchWhenStarted(block)
}

对于您的测试，您可以使用测试范围：

class TestScope(override val coroutineContext: CoroutineContext) : YourCoroutineScope {
    val scope = TestCoroutineScope(coroutineContext)
    override fun launch(block: suspend CoroutineScope.() -> Unit): Job {
        return scope.launch {
            block.invoke(this)
        }
    }
}

现在，由于您的 ViewModel 使用 YourCoroutineScope 类型的范围，并且在上面的示例中，生命周期和测试版本都实现了 YourCoroutineScope 接口，因此您可以在不同情况下使用不同版本的范围，即应用程序 vs测试。

Answer 2

好的，感谢Dapp's 的回答，我能够编写一些似乎正在等待功能正确的测试。

这是我所做的副本:)

enum class MovieApiStatus { LOADING, ERROR, DONE }

class MovieListViewModel(val coroutineScope: ManagedCoroutineScope) : ViewModel() {
//....creating vars, livedata etc.

    init {
        getMovies(pageCount)
    }


    fun getMovies(pageNumber: Int) =

        coroutineScope.launch{
            val getMoviesDeferred =
                MovieApi.retrofitService.getMoviesAsync(page = pageNumber)
            try {
                _status.value = MovieApiStatus.LOADING
                val responseObject = getMoviesDeferred.await()
                _status.value = MovieApiStatus.DONE
                if (_movieList.value == null) {
                    _movieList.value = ArrayList()
                }
                pageCount = pageNumber.inc()
                _movieList.value = movieList.value!!.toList().plus(responseObject.results)
                    .sortedByDescending { it.vote_average }
            } catch (e: Exception) {
                _status.value = MovieApiStatus.ERROR
                _movieList.value = ArrayList()
            }
        }


    fun onLoadMoreMoviesClicked() =
        getMovies(pageCount)

//...nav functions, clearing functions etc.
}

这里是测试用例

@ExperimentalCoroutinesApi
@RunWith(MockitoJUnitRunner::class)
class MovieListViewModelTest {

    @get:Rule
    var instantExecutorRule = InstantTaskExecutorRule()

    private val testDispatcher = TestCoroutineDispatcher()
    private val managedCoroutineScope: ManagedCoroutineScope = TestScope(testDispatcher)
    lateinit var viewModel: MovieListViewModel


    @Before
    fun setup() {
        //resProvider.mockColors()
        Dispatchers.setMain(testDispatcher)
        viewModel = MovieListViewModel(managedCoroutineScope)

    }

    @After
    fun tearDown() {
        Dispatchers.resetMain()
        testDispatcher.cleanupTestCoroutines()
    }

    @ExperimentalCoroutinesApi
    @Test
    fun getMoviesTest() {
        managedCoroutineScope.launch {
            assertTrue(
                "initial List, API status: ${viewModel.status.getOrAwaitValue()}",
                viewModel.status.getOrAwaitValue() == MovieApiStatus.DONE
            )
            assertTrue(
                "movieList has ${viewModel.movieList.value?.size}, != 20",
                viewModel.movieList.value?.size == 20
            )
            assertTrue(
                "pageCount = ${viewModel.pageCount}, != 2",
                viewModel.pageCount == 2
            )
            viewModel.onLoadMoreMoviesClicked()
            assertTrue(
                "added to list, API status: ${viewModel.status.getOrAwaitValue()}",
                viewModel.status.getOrAwaitValue() == MovieApiStatus.DONE
            )
            assertTrue(
                "movieList has ${viewModel.movieList.value?.size}, != 40",
                viewModel.movieList.value?.size == 40
            )

        }
    }
}

使用 Scopes 进行了一些试验和错误。runBlockingTest{} 导致出现“异常：job() 未完成”问题..

我还必须创建一个 viewModel 工厂，以便片段在应用正常运行时创建 viewModel。

Project Repo