单元测试：观察者 onChanged 应该被调用两次而不是一次

Question

为什么在对我的 ViewModel 进行单元测试时得到不同的结果？

我有两个测试。当我单独启动每个测试时没问题，但是当我连续启动所有测试时出现错误。 每次我从 API。我希望android.arch.lifecycle.Observer.onChanged 被调用两次，但第二次测试只调用一次。 当我在第一次测试中将 verify(view, times(2)).onChanged(arg.capture()) 替换为 verify(view, atLeastOnce()).onChanged(arg.capture()) 时，单元测试工作正常。

用户视图模型：

class UserViewModel(
        private val leApi: LeApi
): ViewModel() {
    private val _states = MutableLiveData<ViewModelState>()
    val states: LiveData<ViewModelState>
        get() = _states

    fun getCurrentUser() {
        _states.value = LoadingState
        leApi.getCurrentUser()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(
                        { user -> _states.value = UserConnected(user) },
                        { t -> _states.value = FailedState(t) }
                )
        }
    }
}

用户视图模型测试：

@RunWith(MockitoJUnitRunner::class)
class UserViewModelTest {

    lateinit var userViewModel: UserViewModel

    @Mock
    lateinit var view: Observer<ViewModelState>

    @Mock
    lateinit var leApi: LeApi

    @get:Rule
    val rule = InstantTaskExecutorRule()

    @Before
    fun setUp() {
        RxAndroidPlugins.setInitMainThreadSchedulerHandler { Schedulers.trampoline() }
        userViewModel = UserViewModel(leApi)
        userViewModel.states.observeForever(view)
    }

    @Test
    fun testGetCurrentUser() {
        val user = Mockito.mock(User::class.java)
        `when`(leApi.getCurrentUser()).thenReturn(Single.just(user))
        userViewModel.getCurrentUser()

        val arg = ArgumentCaptor.forClass(ViewModelState::class.java)
        verify(view, times(2)).onChanged(arg.capture())

        val values = arg.allValues

        assertEquals(2, values.size)
        assertEquals(LoadingState, values[0])
        assertEquals(UserConnected(user), values[1])
    }

    @Test
    fun testGetCurrentUserFailed() {
        val error = Throwable("Got error")
        `when`(leApi.getCurrentUser()).thenReturn(Single.error(error))
        userViewModel.getCurrentUser()

        val arg = ArgumentCaptor.forClass(ViewModelState::class.java)
        verify(view, times(2)).onChanged(arg.capture()) // Error occurred here. That's the 70th line from stack trace.

        val values = arg.allValues
        assertEquals(2, values.size)
        assertEquals(LoadingState, values[0])
        assertEquals(FailedState(error), values[1])
    }
}

预期： 所有测试都通过了。

实际：

org.mockito.exceptions.verification.TooLittleActualInvocations: 
view.onChanged(<Capturing argument>);
Wanted 2 times:
-> at com.dev.titi.toto.mvvm.UserViewModelTest.testGetCurrentUserFailed(UserViewModelTest.kt:70)
But was 1 time:
-> at android.arch.lifecycle.LiveData.considerNotify(LiveData.java:109)

Answer 1

我遇到了这个确切的问题。我将测试方式更改为以下（Google recommendations, here are the classes used for following test）：

将协程添加到您的项目中，因为测试助手使用它们：

implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.2.0")
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1")
testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.0'

去掉这一行：

lateinit var view: Observer<ViewModelState>

然后将您的测试更改为以下内容：

private val testDispatcher = TestCoroutineDispatcher()

@Before
fun setup() {
    Dispatchers.setMain(testDispatcher)
    ...
}

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

@Test
fun testGetCurrentUser() {
    runBlocking {
        val user = Mockito.mock(User::class.java)
        `when`(leApi.getCurrentUser()).thenReturn(Single.just(user))
        userViewModel.states.captureValues {
            userViewModel.getCurrentUser()
            assertSendsValues(100, LoadingState, UserConnected(user))
        }
    }
}