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kotlinlang

Hi all :android-wave:,
How to write UT for logic inside Composables?

For stateless UI composables, I can cover them using compose testing.
But, for a stateful composable, how can I test the logic?
Sample code in :thread: .

Example
```@Composable
fun HomeScreen() {
  var state1 by remember {
        mutableStateOf(
            value = "First Name",
        )
  }

  var state2 by remember {
        mutableStateOf(
            value = 123,
        )
  }

  val combinedState = remember(state1, state2) {
    // Some logic which creates a new state by processing the existing states.
  }
}```
In this case, How to test the logic added here?
```// Some logic which creates a new state by processing the existing states.```
One option I can think of is to extract the code into a top level function outside the `HomeScreen` composable and test it.
I would like to know if there are better approaches to structure and test this code. :thank-you-color:

Ideally, hoist the state to make the caller own it and make your component stateless. Otherwise, you’d need to interact with the component via semantics or other input events. 

This is the top most screen level composable.

This composable is only for the state handling.
All UI is rendered using a child composable which is completely stateless.

Sounds like that stuff should be in a view model or presenter or something, not a composable 

Do you mean I can not have states in Composable :thinking_face:?

Any reason to hoist all UI states in the ViewModel if the view model does not require the state?

That’s not what I mean, you can definitely have state in composables. But if you have a bunch of business logic that drives your view layer, and you want to test it separately, that is the whole reason for separating the presentation/view model as a separate architectural layer from the view layer. All these architectural patterns basically exist to solve this problem. 