Hello, I am trying to write screenshot tests for `...

# compose

[Abhinav Sharma]

Hello,
I am trying to write screenshot tests for HorizontalTrayUi() and TrayItemUi()
Its easy to test TrayItemUi() in isolation by mocking TrayItemViewModel and its exposed state flows, but whats the recommended way to test HorizontalTrayUi() as it calls TrayItemUi() which then tries to create a viewModel using Hilt

Here’s the structure

@Composable
fun HorizontalTrayUi(
	trayModel: TrayModle,
	viewModel: TrayViewModel = viewModel()
) {
	Text(...) // title of the tray
	LazyRow(..){
		item -> {
			TrayItemUi(item)
		}
	}
}

@Composable
fun TrayItemUi(
	item: TrayItemModel,
	viewModel: TrayItemViewModel = viewModel()
) {
	......
}

@Pedro Gomez

[Pedro Gomez]

Assume the screenshot testing library will take the screenshot of what's shown on the screen. No matter how many composable views you have inside. If A depends on B and you render A. Your screenshot will show A and B. If you only render B, A will be out of the screenshot scope.

If you want to use test doubles you'll need to pass the view model from the HorizontalTrayUi even if it's used inside TrayItemUi. Looking at the code I think you'll have to modify HorizontalTrayUi API to receive the TrayItemViewModel instances or a factory. Dependency injectors are quite handy for this. You have some examples here: https://github.com/Karumi/KataSuperHeroesCompose

[Abhinav Sharma]

Thanks, I will try using Hilt in tests for injecting TrayItemViewModel — sounds like a good idea
But getting TrayItemViewModel in HorizontalTrayUi() — isn’t sounding good as Composables can be nested to any level and just for tests I cannot pull all viewmodels in root composable methods..

But thanks for the idea - going to dig into Hilt usage for Tests..

[Pedro Gomez]

yeap, that's why dependency injection is so useful 🙂