android - java.lang.IllegalStateException: MaybeRun がないとキャンセル呼び出しは発生しません

Question

ViewModelで簡単にテストしようとしていRobolectricます。

これが私のViewModel

GreetingsViewModel.kt

@FlowPreview
@ExperimentalCoroutinesApi
class GreetingsViewModel : ViewModel() {


    private val greetingsChannel = ConflatedBroadcastChannel<String>()

    /**
     * Whenever greetingsChannel offers a value, prepend `Hello ` with it and return.
     */
    val greetingsResponse = greetingsChannel.asFlow()
        .flatMapLatest { name ->
            flowOf("Helo $name")
        }.asLiveData(viewModelScope.coroutineContext)

    /**
     * To get new greetings
     */
    fun askGreetings(name: String) {
        greetingsChannel.offer(name)
    }
}

ここに私の単体テストファイルがあります

GreetingsViewModelTest.kt

@FlowPreview
@ExperimentalCoroutinesApi
@RunWith(AndroidJUnit4::class)
class GreetingsViewModelTest2 {

    @Test
    fun greeting_askGreetings_getWithName() {
        val testViewModel = GreetingsViewModel()
        testViewModel.askGreetings("john")
        testViewModel.greetingsResponse.getOrAwaitValue().should.equal("Hello john")
    }
}

しかし、テストを実行するとエラーが発生します。

java.lang.IllegalStateException: Cancel call cannot happen without a maybeRun

    at androidx.lifecycle.BlockRunner.cancel(CoroutineLiveData.kt:184)
    at androidx.lifecycle.CoroutineLiveData.onInactive(CoroutineLiveData.kt:245)
    at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:440)
    at androidx.lifecycle.LiveData.observeForever(LiveData.java:232)
    at com.theapache64.twinkill.test.GetOrAwaitValueKt.getOrAwaitValue(getOrAwaitValue.kt:26)
    at com.theapache64.twinkill.test.GetOrAwaitValueKt.getOrAwaitValue$default(getOrAwaitValue.kt:15)
    at com.theapache64.tracktor.ui.activities.test.GreetingsViewModelTest.greeting_askGreetings_getWithName(GreetingsViewModelTest.kt:23)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.robolectric.RobolectricTestRunner$HelperTestRunner$1.evaluate(RobolectricTestRunner.java:546)
    at org.robolectric.internal.SandboxTestRunner$2.lambda$evaluate$0(SandboxTestRunner.java:252)
    at org.robolectric.internal.bytecode.Sandbox.lambda$runOnMainThread$0(Sandbox.java:89)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

理由はありますか？

注: getOrAwaitValue()LiveDataは、 a の値を取得するか、タイムアウトを使用して値が取得されるのを待機する拡張関数です。