测试协程和LiveData：协程结果未反映在LiveData上

Question

我是测试的新手，我想学习如何使用MVVM模式测试协程。我只关注了https://github.com/android/architecture-samples项目，并做了一些更改（删除了远程源）。但是，当测试ViewModel以从存储库中获取数据时，它会继续失败并显示此错误。

Ruby version - 2.5.3
Rails version - 5.2.3

以下是value of : iterable.size() expected : 3 but was : 0 iterable was: [] Expected :3 Actual :0 的测试类，不知道我缺少什么。另外，在模拟存储库时，我可以在打印ViewModel时从中获得预期的结果，它在调用taskRepository.getTasks()

时不会反映在LiveData上

ViewModelTest

loadTasks()

TasksViewModel

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

    private lateinit var tasksViewModel: TasksViewModel

    val tasksRepository = mock(TasksRepository::class.java)

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

    // Executes each task synchronously using Architecture Components.
    @get:Rule
    var instantExecutorRule = InstantTaskExecutorRule()

    @Before
    fun setupViewModel() {
        tasksViewModel = TasksViewModel(tasksRepository)
    }

    @Test
    fun whenLoading_hasListOfTasks() = runBlockingTest {
        val task1 = Task("title1", "description1")
        val task2 = Task("title2", "description2")
        val task3 = Task("title3", "description3")
        `when`(tasksRepository.getTasks()).thenReturn(Result.Success(listOf(
           task1,
           task2,
           task3
        )))

        tasksViewModel.loadTasks()

        val tasks = LiveDataTestUtil.getValue(tasksViewModel.tasks)
        assertThat(tasks).hasSize(3)
    }
}

下面列出了Helper类，我只是从示例项目中复制了相同的类。

LiveDataTestUtil

class TasksViewModel @Inject constructor(
  private val repository: TasksRepository
) : ViewModel() {

  private val _tasks = MutableLiveData<List<Task>>().apply { value = emptyList() }
  val tasks: LiveData<List<Task>> = _tasks

  fun loadTasks() {
    viewModelScope.launch {
      val tasksResult = repository.getTasks()

      if (tasksResult is Success) {
        val tasks = tasksResult.data
        _tasks.value = ArrayList(tasks)
      }
    }
  }
}

MainCoroutineRule

object LiveDataTestUtil {

    /**
     * Get the value from a LiveData object. We're waiting for LiveData to emit, for 2 seconds.
     * Once we got a notification via onChanged, we stop observing.
     */
    fun <T> getValue(liveData: LiveData<T>): T {
        val data = arrayOfNulls<Any>(1)
        val latch = CountDownLatch(1)
        val observer = object : Observer<T> {
            override fun onChanged(o: T?) {
                data[0] = o
                latch.countDown()
                liveData.removeObserver(this)
            }
        }
        liveData.observeForever(observer)
        latch.await(2, TimeUnit.SECONDS)

        @Suppress("UNCHECKED_CAST")
        return data[0] as T
    }
}

Answer 1

事实证明，这是mockito的问题，我有一个较旧的版本，并且发现有一个名为mockito-kotlin的库可以简化here所述的协程测试。然后，我将代码修改为此，并且运行良好。

tasksRepository.stub {
    onBlocking { getTasks() }.doReturn(Result.Success(listOf(task1, task2, task3)))
}