Position Block Support: Add PHP tests

[andrewserong]

What?

Part of #47043 and following on from #46142

Add PHP tests for the position block support.

Why?

• To ensure the block support is outputting styles in an expected way.
• As preparation for backporting the feature to core.

How?

• Add a PHP test file for the position support
• Copy the approach from the layout block support that uses theme switching
• For testing position output, reuse the fluid typography test theme as it opts in to the appearance tools
• Test for:
  • Correct position output
  • Don't output when the theme doesn't support it
  • Don't output when the block doesn't support it
  • Don't output rules when the position type is invalid

Testing Instructions

Check that the PHP tests Github action passes, or run manually via:

npm run test:unit:php -- --filter WP_Block_Supports_Position_Test

[github-actions]

Flaky tests detected in 0bb453e.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4061201904
📝 Reported issues:

• [Flaky Test] should be able to create an hierarchical post without title support #36939 in specs/editor/plugins/custom-post-types.test.js

[aaronrobertshaw]

Thanks for the added tests @andrewserong 👍

I've run the tests locally and they pass as per the Github action. The code looks good to me except for a small copy/paste typo.

Happy to approve this pending the suggested tweak. Nice work!

[andrewserong]

Excellent, thanks for the speedy review and spotting the typo! Committed and enabled auto-merge 👍

[Mamaduka]

I just cherry-picked this PR to the release/15.1 branch to get it included in the next release: 752ec31