Tests: Group tests that depend on Core assets

[lancewillett]

Some PHPUnit tests depend on Core JavaScript and CSS files, so they must remain covered when testing is narrowed for frontend-only changes.

Add an assets group to seven existing test methods covering shortcode regex parity, CSS inlining and hoisting, admin view-transition CSS, and generated script-module files. The annotations allow --group assets selection while keeping every test in its normal suite.

The selection includes the methods identified by the empty-assets experiment in Trac comment 4, plus nearby tests that read assets or require them to exist. Emptying a file does not necessarily fail tests whose expectations are derived from that file.

This PR adds test annotations only. Workflow routing is proposed separately in PR #13523, which depends on this group landing first. Bundled-theme metadata, test fixtures, and build tooling still need normal testing; this group does not establish that every .js or .css change can use reduced coverage.

Trac ticket: https://core.trac.wordpress.org/ticket/65889

Testing notes

Validation on current trunk with PHP 8.3.32, MySQL 9.7.2, and PHPUnit 9.6.36:

• --group assets: 23 tests / 253 assertions passed on both single site and multisite.
• Generated script-module file check explicitly executed: 1 test / 59 assertions passed.
• PHPCS passed all five modified files.
• Assets built with npm run build:dev in Node 24 Docker.

An isolated experiment emptied 1,295 source and generated .js/.css files under src/js/, src/wp-admin/css/, src/wp-admin/js/, src/wp-includes/css/, src/wp-includes/js/, and src/wp-includes/build/ after building. Bundled themes and test fixtures were kept intact.

• Full single-site run: 26,234 tests; full multisite run: 27,074 tests.
• Both runs reproduced the same 10 failures covered by this group: shortcode regex parity, eight late-style-hoisting datasets, and admin view-transition CSS.
• Both also hit Tests_Image_Functions::test_wp_crop_image_with_url. That test still failed alone after restoring assets (error_loading_image: File does not exist? for the remote image), so it was not attributed to asset truncation.
• All 1,295 assets were restored and verified against their original SHA-256 hashes. The restored assets group passed again: 23 tests / 253 assertions.

The full runs were not green: each reported 11 failures and 86 warnings, with 44 single-site skips and 46 multisite skips. The result supports the group for the tested asset paths; it is not a claim of exhaustive coverage for every frontend file.

Use of AI tools

AI assistance: Yes.
Tool: Codex.
Model: GPT-6.
Used for: Auditing asset-dependent tests, adding group annotations, and local validation.

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