用StateFlow测试Android StateFlow，该mapsLatest来自另一个StateFlow，但mapLatest从未触发

Question

所以我有一个ViewModel，我正在尝试单元测试。它使用的是stateIn运算符。我找到了关于如何测试使用stateIn操作符https://developer.android.com/kotlin/flow/test创建的状态流的文档，但是即使我正在收集流，mapLatest也不会触发。

class DeviceConfigurationViewModel(
    val systemDetails: SystemDetails,
    val step: AddDeviceStep.ConfigureDeviceStep,
    val service: DeviceRemoteService
) : ViewModel(), DeviceConfigurationModel {

    @OptIn(ExperimentalCoroutinesApi::class)
    private val _state: StateFlow<DeviceConfigurationModel.State> =
        service.state
            .mapLatest { state ->
                when (state) {
                    DeviceRemoteService.State.Connecting -> {
                        DeviceConfigurationModel.State.Connecting
                    }
                    is DeviceRemoteService.State.ConnectedState.Connected -> {
                        state.sendCommand(step.toCommand(systemDetails))
                        DeviceConfigurationModel.State.Connected
                    }
                    is DeviceRemoteService.State.ConnectedState.CommandSent -> {
                        DeviceConfigurationModel.State.Configuring
                    }
                    is DeviceRemoteService.State.ConnectedState.MessageReceived -> {
                        transformMessage(state)
                    }
                    is DeviceRemoteService.State.Disconnected -> {
                        transformDisconnected(state)
                    }
                }
            }
            .distinctUntilChanged()
            .stateIn(
                viewModelScope,
                SharingStarted.WhileSubscribed(5000), // Keep it alive for a bit if the app is backgrounded
                DeviceConfigurationModel.State.Disconnected
            )

    override val state: StateFlow<DeviceConfigurationModel.State>
        get() = _state

    private fun transformDisconnected(
        state: DeviceRemoteService.State.Disconnected
    ): DeviceConfigurationModel.State {
        return if (state.hasCause) {
            DeviceConfigurationModel.State.UnableToConnect(state)
        } else {
            state.connect()
            DeviceConfigurationModel.State.Connecting
        }
    }

    private fun transformMessage(state: DeviceRemoteService.State.ConnectedState.MessageReceived): DeviceConfigurationModel.State {
        return when (val message = state.message) {
            is Message.AddedToProject -> DeviceConfigurationModel.State.Configured
            is Message.ConfigWifiMessage -> {
                if (!message.values.success) {
                    DeviceConfigurationModel.State.Error(
                        message.values.errorCode,
                        state,
                        step.toCommand(systemDetails)
                    )
                } else {
                    DeviceConfigurationModel.State.Configuring
                }
            }
        }
    }

}

这是我的单元测试。即使我正在收集流量，mapLatest似乎也不会被触发。我正在使用这里的建议，https://developer.android.com/kotlin/flow/test

@OptIn(ExperimentalCoroutinesApi::class)
class DeviceConfigurationViewModelTest {

    private val disconnectedService = mock<DisconnectedService>()

    private val deviceServiceState: MutableStateFlow<DeviceRemoteService.State> =
        MutableStateFlow(DeviceRemoteService.State.Disconnected(disconnectedService, Exception()))

    private val deviceService = mock<DeviceRemoteService> {
        on { state } doReturn deviceServiceState
    }

    private val systemDetails = mock<SystemDetails> {

        on { controllerAddress } doReturn "192.168.1.112"

        on { controllerName } doReturn "000FFF962FE7"

    }

    private val step = AddDeviceDeviceStep.ConfigureDeviceStep(
        44,
        "Thou Shalt Not Covet Thy Neighbor’s Wifi",
        "testing616"
    )

    private lateinit var viewModel: DeviceConfigurationViewModel

    @Before
    fun setup() {
        viewModel = DeviceConfigurationViewModel(systemDetails, step, deviceService)
    }

    @Test
    fun testDeviceServiceDisconnectWithCauseMapsToUnableToConnect() =
        runTest {

            val collectJob = launch(UnconfinedTestDispatcher()) { viewModel.state.collect() }

            deviceServiceState.emit(
                DeviceRemoteService.State.Disconnected(Exception("Something bad happened"))
            )

            assertThat(viewModel.state.value).isInstanceOf(DeviceConfigurationModel.State.UnableToConnect::class.java)
            collectJob.cancel()
        }

}

Answer 1

我认为这是因为viewModelScope在引擎盖下使用了硬编码的主调度程序。

您可以按照在Android文档中的说明来查看如何设置测试的主调度程序。