Not sure if this really is Compose-specific (maybe...

# compose

[sindrenm]

Not sure if this really is Compose-specific (maybe I don't understand kotlinx.coroutines-test properly), but how would I go about unit testing that a separate state updates as a result of TextFieldState changes? I was hoping I could do something like what I have in the thread.

[sindrenm]

class LoginViewModel : ViewModel() {
    init {
        viewModelScope.launch {
            combine(
                snapshotFlow { uiState.username.text },
                snapshotFlow { uiState.password.text },
            ) { username, password -> username.isNotBlank() && password.isNotBlank() }
                .distinctUntilChanged()
                .collect { isFormFilled ->
                    uiState = uiState.copy(
                        signInButtonState = if (isFormFilled) {
                            SignInButtonState.Enabled
                        } else {
                            SignInButtonState.Disabled
                        },
                    )
                }
        }
    }
}

[sindrenm]

@Test
fun `If the form is filled, the Sign In button is enabled`() = runTest {
    val viewModel: LoginViewModel = // ...

    viewModel.uiState.username.edit { insert(0, "AzureDiamond") }
    viewModel.uiState.password.edit { insert(0, "hunter2") }

    advanceUntilIdle()

    assertEquals(SignInButtonState.Enabled, viewModel.uiState.signInButtonState)
}

[Sean Proctor]

Is there a reason you don't calculate that when it's needed? You could add in the uiState: val signInButtonState get() = if (username.isNotBlank() && password.isNotBlank()) SignInButtonState.Enabled else SignInButtonState.Disabled

[sindrenm]

I could do that, but there are other states, too (a SignInButtonState.Loading, for instance, that would need to be set outside.

[Stylianos Gakis]

Can you pass into your ViewModel a custom CoroutineScope which doesn't require you to do all the dance with advanceUntilIdle etc.
Inside the scope of your runTest{} lambda you got access to backgroundScope and you can pass that into the constructor of your ViewModel as of the later versions.

That way you can at least take the ViewModel quirks out of the way.

[sindrenm]

Ideally, yes, but it complicates our current setup with Hilt how these ViewModels are created in production code.

[sindrenm]

Just did it for the sake of checking if the test would pass, and interestingly, now all my other tests there fail. 😅

[Stylianos Gakis]

Does it? Can you try to default to whatever you were defaulting to before as well, but leave it open for overriding for tests?

[sindrenm]

internal class LoginViewModel @Inject constructor(
    // ...
    coroutineSScope: CoroutineScope,
) : ViewModel(coroutineSScope) {
    // still using this.viewModelScope in the class body
}

[sindrenm]

Defaulting to the ViewModel.viewModelScope extension doesn't seem straight-forward, either.

[sindrenm]

(That's not just an IDE bug, it also doesn't compile.)

[Stylianos Gakis]

Yeah that doesn't work I think. But you can default to what viewModelScope did internally, which was Dispatchers.main.immediate + SupervisorScope()

[Albert Chang]

You need this for snapshotFlow to work in unit tests.

[sindrenm]

Yeah, setting the default to what ViewModel does internally does work, but it feels a little bad. If it turns out that this setup is buggy and gets fixed internally in androidx, I would need to follow up on those fixes in my own code, too.

[sindrenm]

Oh, thanks, @Albert Chang! I'll try that out!

[sindrenm]

That did the trick:

@Test
fun `If the form is filled, the Sign In button should be enabled`() = runTest {
    val viewModel = LoginViewModel(
        repository = FakeAuthRepository(loginResult = Unit.right()),
        tracker = fakeTracker,
        networkConfigRepository = FakeNetworkConfigRepository(),
    )

    viewModel.uiState.username.edit { insert(0, "AzureDiamond") }
    viewModel.uiState.password.edit { insert(0, "hunter2") }

    Snapshot.sendApplyNotifications()

    assertEquals(SignInButtonState.Enabled, viewModel.uiState.signInButtonState)
}

Thanks!

[sindrenm]

Although why wouldn't I also need advanceUntilIdle() here? 🤔