Remove StableDecoupledTest

Thanks for opening this! +1 from me. ;)

We need a new git rm patch now that #3033734: Horizontal scrollbar on /admin/modules landed.

Sweet, thanks! I'll RTBC when the bot comes back green. ;)

Also, wondering about the fate of this test in the 9.0.x branch. Do we still need it there, too? If so, can/should we make any improvements to it? Seems that'd be a separate issue from this one. In particular:

A) $this->assertEmpty($files_inherited_from_stable); The default PHPUnit message when this assertion fails is just "Failed asserting that an array is empty." In #3033734 I had to add some debugging code to the test when running it locally to confirm system.admin.css was indeed the problem. It'd be really nice if the test output told us that directly.

B) If this test is going to fail (by design) whenever stable diverges from core markup, can we add some more comments to help folks understand how to properly fix the test in this (potentially common) case of failure? I.e. make it more obvious that 3033734.49_51.interdiff.txt is the intended solution whenever stable and core intentionally diverge?

C) Patch #3033734-49 kept stable and system's CSS in sync, but forgot to change stable9. It passed all tests (except the watchful eyes of @xjm). ;) Do we intend to notice if stable9 is getting out of sync? Seems like we don't want that, since we *want* the core CSS to diverge from stable9. But I wanted to raise it to be sure.

D) There are a handful of typos in the comments.

Should I open followup issue(s) for these, or should we commit #2 to the 9.0.x branch? ;)

Thanks again!
-Derek

#4 is definitely RTBC for the 9.1.x branch.

#2 would be RTBC for 9.0.x if we're going to backport this. ;) If not, guess I'll open a follow-up for my list in #5.

Thanks!
-Derek

Committed to 9.1.x. Thanks StableDecoupledTest for your service.

I'm not totally sure about backporting the removal to 9.0.x. It mostly served its purpose prior to beta1, but I think we should keep it around in case something else comes up WRT the 9.0 theme changes. Failures like the one from #3033734: Horizontal scrollbar on /admin/modules aren't going to be something we run into because we're at the point (in beta-almost-RC) where core theming changes/bugfixes will only be happening in 9.1.x.

Stable 9 is also in beta now which means it's not changing. Stable 10 will be updated with all the bug fixes and improvements we make to module CSS and templates in D9, including this one from system.module. Edit: Also, meant to say there's no need for an equivalent test for Stable 9, because core themes don't inherit from it either. They just get module CSS and templates directly.

Thanks!

Cool, thanks.
Agreed on no test for stable9 (by design).
Duly noted on keeping the test alive in 9.0.x.
Follow-up for the other improvements from #5 at #3138739: Improve StableDecoupledTest in the 9.0.x branch

Thanks again!
-Derek