I'm trying to write some tests asserting the state of my snapshot state. It's testing within a ViewM...

# compose

[Colton Idle]

I'm trying to write some tests asserting the state of my snapshot state. It's testing within a ViewModel so it (unfortunately) uses viewModelScope.launch (which i hope doesn't derail the discussion.

But essentially, this test should pass, but it doesn't. What's the best way to wait for my snapshotState to return a value to assert upon it?

@Test
fun `vm state is right`() {
  runBlocking {
    val myVm = HomeScreenViewModel(FakeGetHomeScreenUseCase())
    myVm.populateItemsWithOneItem()
    assertEquals(1, myVm.state.items.size)
  }
}

[Colton Idle]

My VM:

fun populateItemsWithOneItem() {
  viewModelScope.launch {
    state.items.addAll(getHomeScreenUseCase.getItems())
  }
}

[Zach Klippenstein (he/him) [MOD]]

Wait for whatever dispatcher your coroutine is using to get to idle. If compose-based, use Compose’s runOnIdle, otherwise Espresso.onIdle should work

[Zach Klippenstein (he/him) [MOD]]

Espresso.onIdle waits for the main queue to be idle, which is what viewModelScope dispatches to I believe

[Colton Idle]

Do you know if I need to be writing androidTests with this or should this work in a unit test?

Reason I ask is because I tried in a unit test and was met with

FINGERPRINT must not be null

lol. idk what that is

[Colton Idle]

Actually. I guess I'm using dispatchers.main. But I can't really find a way to awaitIdle on the main dispatcher. Maybe im missing something basic here (sorry im still new to testing this stuff)

[Colton Idle]

but it seems pretty basic like I should be able to test this... right?

[Zach Klippenstein (he/him) [MOD]]

Compose UI’s testing framework uses some hackery to await idle with Robolectric - a combination of Espresso.onIdle and explicitly checking internal compose state.

If you’re just waiting for a coroutine launcher on main, I would expect Espresso.onIdle would be enough, but then I would assume you’d need to use the Main dispatcher as well

[Colton Idle]

Hm. Still no dice. I guess I'm going to give up here. Really not sure how testing something like this ends up being such a pain. 😭

[Arjun Achatz]

Have you tried injecting your dispatcher? Then you can swap it out for anything

[Colton Idle]

Even if I inject my dispatcher, dont I still need to wait somehow?