Does anyone know how to unit test code which uses ...

# coroutines

[muthuraj]

Does anyone know how to unit test code which uses Flow.debounce? The unit test doesn't wait until debounce is completed. It should actually advance the delay since I'm using runBlockingTest as per the documentation, but that doesn't happen. Here is an example that reproduces my case.

class DebounceTest(scope: CoroutineScope) {
    private val stateFlow = MutableStateFlow("")
    val resultFlow = MutableStateFlow("")

    init {
        stateFlow.debounce(500)
            .onEach {
                resultFlow.value = it
            }
            .launchIn(scope)
    }

    fun search(text: String){
        stateFlow.value = text
    }
}

@Test
    fun debounceTest() = runBlockingTest {
        val sut = DebounceTest(this)
        sut.search("test")
        assertThat(sut.resultFlow.value).isEqualTo("test")
    }

The test here fails saying the actual value of resultFlow.value is empty string instead of test

[mateusz.kwiecinski]

If you want to manipulate time in your test you have to do that manually by calling advanceTimeBy(500) after sut.search("test")
runBlockingTest allows you to control the time but doesn’t do anything automatically during the test execution.

[muthuraj]

Thanks, advancedtimeBy works, but I'm blocked by this issue
https://github.com/Kotlin/kotlinx.coroutines/issues/1531
I'm getting Test finished with active jobs error since the job inside the DebounceTest init block is not canceled.
And I can't cancel it manually since my actual code is Android ViewModel and it uses viewModelScope inside it.

[Nick Allen]

I'm not sure the linked issue is related since viewModelScope creates its own scope (unless you create the TestCoroutineScope with viewModelScope). There's also a workaround in the issue. What's stopping you from just calling cancel on viewModelScope? If you are still stuck, maybe you could post a trivial example to show how you are setting up your unit test?

[muthuraj]

@Nick Allen I fixes the issue. The issue was, I was using two different `TestCoroutineDisoatcher`'s and that caused this issue. I used the same diaptcher I pass to Viewmodel to start runBlockingTest and it worked fine after that.

https://stackoverflow.com/a/67897542