单元测试新的Kotlin coroutine StateFlow

Question

我正在尝试它，在尝试单元测试我的ViewModel时遇到了一个问题。我想要实现的目标：测试我的stateflow在我的ViewModel中以正确的顺序接收所有状态值。

我代码如下：

ViewModel：

class WalletViewModel(private val getUserWallets: GetUersWallets) : ViewModel() {

val userWallet: StateFlow<State<UserWallets>> get() = _userWallets
private val _userWallets: MutableStateFlow<State<UserWallets>> =
    MutableStateFlow(State.Init)

fun getUserWallets() {
    viewModelScope.launch {
        getUserWallets.getUserWallets()
            .onStart { _userWallets.value = State.Loading }
            .collect { _userWallets.value = it }
    }
}

    @Test
fun `observe user wallets ok`() = runBlockingTest {
    Mockito.`when`(api.getAssetWallets()).thenReturn(TestUtils.getAssetsWalletResponseOk())
    Mockito.`when`(api.getFiatWallets()).thenReturn(TestUtils.getFiatWalletResponseOk())

    viewModel.getUserWallets()

    val res = arrayListOf<State<UserWallets>>()
    viewModel.userWallet.toList(res) //doesn't works

    Assertions.assertThat(viewModel.userWallet.value is State.Success).isTrue() //works, last value enmited
}

java.lang.IllegalStateException: This job has not completed yet
    at kotlinx.coroutines.JobSupport.getCompletionExceptionOrNull(JobSupport.kt:1189)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest(TestBuilders.kt:53)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest$default(TestBuilders.kt:45)
    at WalletViewModelTest.observe user wallets ok(WalletViewModelTest.kt:52)
....

编辑：作为一个临时解决方案，我将它作为一个实时数据进行测试：

    @Captor
    lateinit var captor: ArgumentCaptor<State<UserWallets>>

    @Mock
    lateinit var walletsObserver: Observer<State<UserWallets>>

    @Test
    fun `observe user wallets ok`() = runBlockingTest {
        viewModel.userWallet.asLiveData().observeForever(walletsObserver)

        viewModel.getUserWallets()

        captor.run {
            Mockito.verify(walletsObserver, Mockito.times(3)).onChanged(capture())
            Assertions.assertThat(allValues[0] is State.Init).isTrue()
            Assertions.assertThat(allValues[1] is State.Loading).isTrue()
            Assertions.assertThat(allValues[2] is State.Success).isTrue()
        }
    }

Answer 1

SharedFlow/Stateflow是热流，正如文档中所述，共享流之所以称为热流，是因为它的活动实例独立于收集器的存在而存在。这意味着启动流的收集的作用域不会自行完成。

要解决这个问题，您需要取消collect被调用的范围，由于测试的范围是测试本身，取消测试是不合适的，所以您需要的是在另一个作业中启动它。

@Test
fun `Testing a integer state flow`() = runBlockingTest{
    val _intSharedFlow = MutableStateFlow(0)
    val intSharedFlow = _intSharedFlow.asStateFlow()
    val testResults = mutableListOf<Int>()

    val job = launch {
        intSharedFlow.toList(testResults)
    }
    _intSharedFlow.value = 5

    assertEquals(2, testResults.size)
    assertEquals(0, testResults.first())
    assertEquals(5, testResults.last())
    job.cancel()
}

您的特定用例：

@Test
fun `observe user wallets ok`() = runBlockingTest {
    whenever(api.getAssetWallets()).thenReturn(TestUtils.getAssetsWalletResponseOk())
    whenever(api.getFiatWallets()).thenReturn(TestUtils.getFiatWalletResponseOk())

    viewModel.getUserWallets()

    val result = arrayListOf<State<UserWallets>>()
    val job = launch {
        viewModel.userWallet.toList(result) //now it should work
    }

    Assertions.assertThat(viewModel.userWallet.value is State.Success).isTrue() //works, last value enmited
    Assertions.assertThat(result.first() is State.Success) //also works
    job.cancel()
}

两件重要的事情：

1. 始终取消创建的作业，以避免java.lang.IllegalStateException：此作业尚未完成
2. 因为这是一个状态流，所以当开始收集时(ToList)您会收到最后一个状态。但是，如果您首先开始收集并在调用函数ViewModel.getUserWallets()之后，那么在result列表中，您将拥有所有状态，以防您也想测试它。