android - 单元测试使用 ViewModelScope.launch 调用具有延迟的挂起函数的 ViewModel 方法

Question

在我的 ViewModel我有一个 onTextChanged通过 EditText 上的数据绑定(bind)调用的方法.在那里我使用viewModelScope.launch{}开始 suspend功能。在那个函数中，我延迟了 500 毫秒。现在我如何测试 onTextChanged方法？我尝试的一切总是在延迟完成之前完成测试。我试过 runBlockingTest , TestCoroutineDispatcher和 runBlocking .

文本观察者:

override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
        searchJob = if (searchJob?.isActive == true) {
            searchJob?.cancel()
            viewModelScope.launch { search(s.toString()) }
        } else {
            viewModelScope.launch { search(s.toString()) }
        }
    }

搜索方法:

 private suspend fun search(query: String) {
            delay(500)
            searchUseCase(SearchParams(query)).fold({

            }, {

            })
    }

考试:

    @Test
    fun `Search is fired after 500ms when text is changed`()  = runBlockingTest {
        val viewModel = ViewModel(useCase)
        viewModel.onTextChanged("test", 0, 0, 0)

        //TODO assert time was 500ms or more

        //This fails
        coVerify(exactly = 1) { useCase.invoke(any()) }
    }

Answer 1

谷歌推荐的是，你应该以某种方式注入(inject) CoroutineDispatcher到您的 View 模型，以便您可以在测试期间更改它。

class MainViewModel(
    private val dispatcher: CoroutineDispatcher = Dispatchers.Default
) : ViewModel() {

    private var _userData: MutableLiveData<Any> = MutableLiveData<Any>()
    val userData: LiveData<Any> = _userData

    fun savedDelayed() = viewModelScope.launch {
        delay(1000)
        saveSessionData()
    }

    suspend fun saveSessionData() {
        viewModelScope.launch(dispatcher) {
            _userData.value = "some_user_data"
        }
    }
}

@ExperimentalCoroutinesApi
class MainViewModelTest {

    private val testDispatcher = TestCoroutineDispatcher()

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

    @get:Rule
    var instantExecutorRule = InstantTaskExecutorRule()

    @Test
    fun testsSaveSessionData() = runBlockingTest {
        val mainViewModel = MainViewModel(testDispatcher)
      
        mainViewModel.savedDelayed()
        testDispatcher.advanceUntilIdle()
      
        val userData = mainViewModel.userData.value
        assertEquals("some_user_data", userData)
    }

}

代码粘贴自中篇文章，并针对您的用例进行了修改。请阅读文章以获得进一步的解释:
https://medium.com/swlh/unit-testing-with-kotlin-coroutines-the-android-way-19289838d257