Hello, what is the goody way to test a function th...

# coroutines

[pdegand]

Hello, what is the goody way to test a function that's consuming a channel ?
My function looks like this :

suspend fun start(channel: ReceiveChannel<Event>) {
  launch(coroutineContext) {
    for (event in channel) {
      val view = // do something with each the event
      withContext(context = UI) {
        _evenementLiveData.value = view
      }
    }
  }
}

and my test looks like this :

@Test
fun testStart() = runBlocking {
  //given
  val channel = ConflatedChannel<Event>()
  val observer = mock<Observer<EvenementDetailView>>()
  presenter.evenementLiveData.observeForever(observer)

  val evenement = // create an event

  //when
  presenter.start(channel)
  channel.send(event)


  //then
  assertThat(presenter.evenementLiveData.value).isEqualTo(expectedView)
}

However, as my method start is launching a coroutine, the assertion in the UT is run before the consumption of the event sent into the channel.
I tried to remove the launch { } inside the start() function, but without it, the runBlocking coroutine of the UT is suspended on presenter.start() because of the for loop inside the start() function.

Am I doing something really wrong here in the start() function or is this a bad design that is hard to unit test or am I simply missing a point somewhere ?
Thx

[gildor]

It looks wrong to just.call launch inside of suspend function without join

[gildor]

You actually start you launch and do not wait for result just return

[gildor]

It's actually not clear how you can test this function with current design

[gildor]

Instead you can wrap function to launch in tests os something similar to send events to channel and listen at the same time

[pdegand]

Thx @gildor, i removed the launch in the suspend fun start() function, and I wrapped the call to start() in the unit test with launch(Unconfined) and now it's working great

[louiscad]

It does not actually consumes the channel since you use a regular for loop that doesn't close the channel like consumeEach or wrapping with consume would do