Add unit tests for useConstrainedTabbing

[afercia]

Description

Related: #47426
Related: #34836

#34836 refactored useConstrainedTabbing but missed to add unit test for the specific use case the refactoring was meant to cover, see #34681.
There should be also some test for the basic functionality of the hook.

It would be great to add a few tests, also noting that some of the other hooks do have tests. I tried in the context of #47426 but my knowledge is limited and I have no idea how to make the hook actually run in a test (it uses useRefEffecta internally). any help would be greatly appreciated.

Step-by-step reproduction instructions

See the hook doesn't have unit tests.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[afercia]

Removing myself as assignee for this issue. It's still a valid problem though.
As mentioned in the attempted PR #48736 I doubt the current implementation is testable because it relies on a native browser behavior that is hardly testable.

Overall, I'm not sure (to be fair) that any non-testable code should be merged in this project.
I'd appreciate any thoughts and feedback Cc @WordPress/gutenberg-core

[ciampo]

One option is to use a real browser environment to run such tests (ie. Playwright) — the quickest way could be to add a suite of e2e tests.

[afercia]

@ciampo thabks for your feedback. E2e tests would test the browser behavior. The whole point here is that the current implementation relies on native browser behaviors that may unexpectedly differ and they did already led to bugs we had to fix. There have been a few with Safari for example.

I do realize it's time consuming but if you check the previous implementation before #34681 / #34836 it was more 'under control' and more testable. It was changed because of a specific case that could have been addressed in a different way, keeping the implementation under control. Instead, it now relies on browser behavior.