test: fix run css playground with legacy sass

[sapphi-red]

Description

Built on top of #18945

Since #18636, the legacy sass tests for playground/css was not run because playground/css/__tests__/sass-legacy/sass-legacy.spec.ts was missing. This PR adds that.

Also this PR extracts sass related tests in a different file to skip running other tests for sass-legacy.spec.ts and sass-modern.spec.ts.

old description

Also this PR does the following changes to reduce flaky fails.

• makes HMR related tests to be only run in css.spec.ts
  • Without this change, all css.spec.ts and sass-modern.spec.ts and sass-legacy.spec.ts tries to change the file and fails sometimes.
• make sass related tests to expect either the expected value before HMR or the expected value after HMR
  • Without this change, the test fails when css.spec.ts changes the file and other tests observes the changed file.
• only run sass related tests in sass-*.spec.ts
  • This is just to reduce the places that needs to write expectToBeEither and also to reduce duplicated test runs.

[bluwy]

I'm not really sure about expectToBeEither, it feels like it could make tests harder to debug if it fails 🤔 Should the HMR tests do cleanup instead so it returns to original? Are the tests also running serially too?

[sapphi-red]

Should the HMR tests do cleanup instead so it returns to original? Are the tests also running serially too?

The tests (css.spec.ts, sass-modern.spec.ts, sass-legacy.spec.ts) are running in parallel because they are different files. So adding a cleanup won't solve the problem here. I thought about only running these test files serially, but didn't find a way to do it.

[hi-ogawa]

the test fails when css.spec.ts changes the file and other tests observes the changed file.

Does adding css-legacy to this help? I think I made this to separate sources between test variants.

vite/playground/vitestGlobalSetup.ts

Lines 44 to 47 in c28df71

	// also setup dedicated copy for "variant" tests
	for (const [original, variants] of [
	['css', ['sass-modern', 'sass-modern-compiler']],
	['css-sourcemap', ['sass-modern', 'sass-modern-compiler']],

[sapphi-red]

Oh, I wasn't aware of that! Let me try that.

[sapphi-red]

Yep, it works 👍