I am trying to test a class that is a

CoroutineScope

and is testing a flow emitted from a fake implementation of another class. However, the flow does not seem to emit the data i assign it to stream. What would you think the problem might be?

private val mainThreadSurrogate = newSingleThreadContext("UI thread")

    @Before
    fun setUp() {
        Dispatchers.setMain(mainThreadSurrogate)
    }

    @After
    fun tearDown() {
        Dispatchers.resetMain() // reset the main dispatcher to the original Main dispatcher
        mainThreadSurrogate.close()
    }

    @Test
    fun testTest(): Unit = runBlocking {
        launch(Dispatchers.Main) {
            val recorder = FakeRecordingsHandler()
            val sut = SomeClass(recorder, this.coroutineContext)
            recorder.currentTrack = flow { emit(DEMO_TRACK) }
            val isCurrentTrack = sut.isCurrentTrack(DEMO_TRACK.id)
            assertTrue(isCurrentTrack)
        }
    }
//    class SomeClass(
//        private val recorder: RecordingsHandler,
//        override val coroutineContext: CoroutineContext
//    ) : VoiceRecorder, CoroutineScope {
//
//        private var currentTrackId: String? by mutableStateOf(null)
//
//        init {
//            launch {
//                recorder.currentTrack.distinctUntilChanged().collect { demoTrack ->
//                    currentTrackId = demoTrack?.id
//            }
//         }
//
//        override fun isCurrentTrack(id: String) = currentTrackId == id
//    }

You are collecting from

currentTrack

in

SomeClass

construction, before

currentTrack

is re-assigned. Try assigning first. If you want to control when the item is emitted, then you can emit into a MutableShareFlow (I'd recommend that anyways).

Unfortunatly that does not seem to work as well, i tried with

MutableSharedFlow

and

MutableStateFlow

as well. Also Tried using

runTest { }

the init block is called but the the code inside launch block is not.

@Test
    fun testTest(): Unit = runTest {
        //launch(Dispatchers.Main) {
            val recorder = FakeRecordingsHandler()
            recorder.currentTrack = MutableStateFlow(DEMO_TRACK)
            val sut = VoiceRecorderViewModel(recorder, this.coroutineContext)
            val isCurrentTrack = sut.isCurrentTrack(DEMO_TRACK.id)
            assertTrue(isCurrentTrack)
       // }
    }

The default dispatcher of

runTest

does not immediately run scheduled coroutine work. You'll want to call

runCurrent

before verifying so that the

launch

code inside

init

actually starts.