[Compose] Unable to capture a screenshot when there is more than 1 root node.

What

This is more of a feature request - allow capturing screenshot with multiple root nodes. Multiple root nodes would typically mean there's a Popup being shown on the screen.

Steps to reproduce

Render some conventional @Composables
Render Popup on the screen, for example DropdownMenu.
Use ScreenshotTest.compareScreenshot(node: SemanticsNodeInteraction, name: String? = null) to capture and compare screenshots.

Resulting in the following error:

java.lang.AssertionError: Failed to capture a node to bitmap.
Reason: Expected exactly '1' node but found '2' nodes that satisfy: (isRoot)
Nodes found:
1) Node #597 at (l=0.0, t=66.0, r=1080.0, b=1532.0)px
Has 2 children
2) Node #608 at (l=0.0, t=0.0, r=706.0, b=389.0)px
Has 1 child

Proposal

Introduce ScreenshotTest.compareScreenshot(nodeCollection: SemanticsNodeInteractionCollection, name: String? = null) to allow passing in multiple nodes. First node in collection should likely define output screenshot dimensions, the rest nodes can be applied upon the result of previous application. Here's the example where 1 is the first node, 2 is applied upon 1, 3 is applied upon 1+2:


 ┌───────────────┬────────┬──────────────────────┐
 │               │        │                      │
 │               │        │                      │
 │               │        │                      │
 │               │        │                      │
 │               │        │                      │
 │               │        │                      │
 │        2      │        │                      │
 │               │        │                      │
 │               │        │                      │
 │               │        │                      │
 │               │        │      3               │
 │               │        │                      │
 │               │        │                      │
 ├───────────────┼────────┘                      │
 │               │                               │
 │               │                               │
 │               │                               │
 │               │                               │
 │               │                               │
 │        1      │                               │
 │               │                               │
 │               └───────────────────────────────┤
 │                                               │
 │                                               │
 │                                               │
 │                                               │
 │                                               │
 └───────────────────────────────────────────────┘

Version of the library

5.11.2

@pedrovgs I'm wondering if you'd be interested in me making such contribution to the library?

pedrovgs / Shot