android - 如何测试启动 viewModelScope 协程的 ViewModel 函数？安卓 Kotlin

Question

我试图找出在函数成员上测试这种类型的最简单方法，我见过更复杂的情况，例如 Coroutines - unit testing viewModelScope.launch methods但没有解决

ListScreenViewModel.kt

@HiltViewModel
class ListScreenViewModel @Inject constructor(): ViewModel() {

    private var _itemsNumber = mutableStateOf(0)

    private var _testList = mutableStateOf(listOf<String>())
    val testList = _testList

    fun addItem() {
        viewModelScope.launch {
            _itemsNumber.value++
            _testList.value += (
                "Item ${_itemsNumber.value}"
                )
        }
    }
}

ListScreenViewModelTest.kt

class ListScreenViewModelTest{

    private lateinit var viewModel: ListScreenViewModel

    @Before
    fun setup(){
        viewModel = ListScreenViewModel()
    }

    @Test
    fun `add an item to the list of items`(){
        val numberOfItems = viewModel.testList.value.size
        viewModel.addItem()
        assert(viewModel.testList.value.size == numberOfItems+1)
    }
}

Error message

Exception in thread "Test worker" java.lang.IllegalStateException: Module with the Main dispatcher had failed to initialize. For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used

Answer 1

你需要使用一个叫做 TestCoroutineDispatcher 的东西。在本地单元测试期间以及使用它的最佳方式创建 Rule .
您可以在此处详细阅读:https://developer.android.com/codelabs/advanced-android-kotlin-training-testing-survey#3
我建议您通过整个代码实验室。这将非常有帮助。
更新版本 1.6.1 :
基于此迁移指南:https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-test/MIGRATION.md

testImplementation ("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.6.1") {
        // https://github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-debug#debug-agent-and-android
        exclude group: "org.jetbrains.kotlinx", module: "kotlinx-coroutines-debug"
    } 

然后在您的测试目录中创建这样的规则，注意 StandardTestDispatcher改变:

@ExperimentalCoroutinesApi
class MainCoroutineRule(private val dispatcher: TestDispatcher = StandardTestDispatcher()) :
    TestWatcher() {

    override fun starting(description: Description?) {
        super.starting(description)
        Dispatchers.setMain(dispatcher)
    }

    override fun finished(description: Description?) {
        super.finished(description)
        Dispatchers.resetMain()
    }
}

像这样使用，注意 runTest的用法& advanceUntilIdle :

@OptIn(ExperimentalCoroutinesApi::class)
class ListScreenViewModelTest {

    @ExperimentalCoroutinesApi
    @get:Rule
    var mainCoroutineRule = MainCoroutineRule()

    private lateinit var viewModel: ListScreenViewModel

    @Before
    fun setUp() {
        viewModel = ListScreenViewModel()
    }


    @Test
    fun `add an item to the list of items`() = runTest {
        val numberOfItems = viewModel.testList.value.size
        viewModel.addItem()
        advanceUntilIdle()
        assert(viewModel.testList.value.size == numberOfItems + 1)
    }
}

原答案:
解决方案
添加此依赖项:

 testImplementation ("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.5.2") {
        // https://github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-debug#debug-agent-and-android
        exclude group: "org.jetbrains.kotlinx", module: "kotlinx-coroutines-debug"
    }

然后在您的测试目录中创建这样的规则:

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.test.TestCoroutineDispatcher
import kotlinx.coroutines.test.TestCoroutineScope
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.setMain
import org.junit.rules.TestWatcher
import org.junit.runner.Description

@ExperimentalCoroutinesApi
class MainCoroutineRule(val dispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()) :
    TestWatcher(),
    TestCoroutineScope by TestCoroutineScope(dispatcher) {

    override fun starting(description: Description?) {
        super.starting(description)
        Dispatchers.setMain(dispatcher)
    }

    override fun finished(description: Description?) {
        super.finished(description)
        cleanupTestCoroutines()
        Dispatchers.resetMain()
    }
}

像这样使用它:

import kotlinx.coroutines.ExperimentalCoroutinesApi
import org.junit.Before
import org.junit.Rule
import org.junit.Test

class ListScreenViewModelTest {

    @ExperimentalCoroutinesApi
    @get:Rule
    var mainCoroutineRule = MainCoroutineRule()

    private lateinit var viewModel: ListScreenViewModel

    @Before
    fun setup(){
        viewModel = ListScreenViewModel()
    }

    @Test
    fun `add an item to the list of items`(){
        val numberOfItems = viewModel.testList.value.size
        viewModel.addItem()
        assert(viewModel.testList.value.size == numberOfItems+1)
    }
}