PublishSubject 和 TestScheduler 的问题，未发出项目

Question

我一直面临着主题和 TestScheduler 的问题。如果我使用 Trampoline 调度程序，我的测试会通过，但是如果我使用 TestScheduler，它们会由于某种原因失败。

这是我的示例测试和相关课程。

@RunWith(MockitoJUnitRunner::class)
class DemoViewModelTest  {


    //Error Mocks
    private val actionsStream: PublishSubject<DemoContract.ViewEvent> = PublishSubject.create()

    private lateinit var viewModel: DemoViewModel

    private val handler = mock(DemoContract.Handler::class.java)

    @Before
    fun setup() {
        viewModel = DemoViewModel(schedulersProvider, handler)
        viewModel.viewEventsStream = actionsStream
    }

    @Test
    fun testUpdateCounter() {
        actionsStream.onNext(DemoContract.ViewEvent.UpdateClick)
        testScheduler.triggerActions()
        verify(handler).onUpdate()

    }


    protected var testScheduler = TestScheduler()

    protected var schedulersProvider: SchedulersProvider = object : SchedulersProvider() {
        override fun mainThread(): Scheduler {
            return testScheduler
        }

        override fun io(): Scheduler {
            return testScheduler
        }

        override fun computation(): Scheduler {
            return testScheduler
        }

        override fun newThread(): Scheduler {
            return testScheduler
        }

        override fun trampoline(): Scheduler {
            return testScheduler
        }

        override fun single(): Scheduler {
            return testScheduler
        }
    }
}

还有我的 ViewModel 类

class DemoViewModel (val schedulersProvider: SchedulersProvider, val handler:DemoContract.Handler) : DemoContract.ViewModel() {

    var viewEventsStream: Observable<DemoContract.ViewEvent>? = null
        set(value) {
            field = value
            subscribeToViewEvents()
        }

    private fun subscribeToViewEvents() {
        viewEventsStream?.let {
            it.subscribeOn(schedulersProvider.io())
                .observeOn(schedulersProvider.mainThread())
                .subscribe(object:Observer<DemoContract.ViewEvent>{
                    override fun onComplete() {

                    }

                    override fun onSubscribe(d: Disposable) {
                    }

                    override fun onNext(t: DemoContract.ViewEvent) {
                        onViewEvent(t)
                    }

                    override fun onError(e: Throwable) {
                    }

                })

        }
    }
     fun onViewEvent(event: DemoContract.ViewEvent) {
        when (event) {
            is DemoContract.ViewEvent.UpdateClick -> {
               handler.onUpdate()
            }
        }
    }

}

我的合同类是

interface DemoContract {
        abstract class ViewModel

        sealed class ViewEvent {
            object UpdateClick : ViewEvent()
        }

        interface Handler{
            fun onUpdate()
        }
    }

关于这个的一些事情，如果我更换

viewModel.viewEventsStream = actionsStream

和

viewModel.viewEventsStream = Observable.just(DemoContract.ViewEvent.Update)

这个测试通过了。

有人可以对此有所了解，提前致谢。这是最小的可运行项目

Answer 1

非常感谢@akarnokd 为我指明了正确的方向。事实证明，这是PublishSubject正在添加的订阅者（subscribeActual调用）和我在测试中触发的 onNext 调用之间的竞争条件。onNext调用在前者发生之前返回。

解决方案是triggerActions在订阅后立即显式调用两次，在发射后立即调用一次。

改变这个

    @Before
    fun setup() {
        viewModel = DemoViewModel(schedulersProvider, handler)
        viewModel.viewEventsStream = actionsStream
    }

到

    @Before
    fun setup() {
        viewModel = DemoViewModel(schedulersProvider, handler)
        viewModel.viewEventsStream = actionsStream
        testScheduler.triggerActions()
    }