Tests: Ensure block support tests are resilient to equivalent HTML changes

[sirreal]

This PR must wait until the previous WordPress version is 6.9.

What?

Instead of using fragile string equality comparisons, this relies on HTML comparisons with Core's assertEqualHTML. This is a semantic comparison of the HTML that is resilient to syntactic differences between equivalent text like & vs ' (which caused problems in the tests).

This prevents the issue that appeared in Gutenberg tests after WordPress/wordpress-develop#10143 was merged.

This reverts commit 7e69ee6 from PR #72236 and implements an alternate approach.

Testing Instructions

CI passes.

[github-actions]

Flaky tests detected in 3d624fb.
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/19041545962
📝 Reported issues:

• [Flaky Test] ensures List View global shortcut works properly #51533 in /test/e2e/specs/editor/various/list-view.spec.js

[github-actions]

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Co-authored-by: ntsekouras <[email protected]>

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[sirreal]

These could become the ' character for more legible tests:

Suggested change

	'expected_wrapper' => '<div class="has-background" style="background-image:url(&#039;https://example.com/image.jpg&#039;);background-size:cover;">Content</div>',
	'expected_wrapper' => '<div class="has-background" style="background-image:url(\'https://example.com/image.jpg\');background-size:cover;">Content</div>',

[ntsekouras]

Thanks for the PR! I thought we had tried that before when investigating and the CI didn't pass. Wasn't that the case?

CI passes.

The difference between now and back then is that the previous failures were from PHP previous major version, which as of #72506 they are not run on GB PR before merged. Have you tested those jobs somehow?

[sirreal]

The difference between now and back then is that the previous failures were from PHP previous major version, which as of #72506 they are not run on GB PR before merged. Have you tested those jobs somehow?

Thank you for noticing that! Indeed, the test method was unavailable in the previous version and we see an error:

Error: Call to undefined method WP_Block_Supports_Background_Test::assertEqualHTML()

This change would be good to make but unfortunately we'll have to wait 🙂