[wp-trac] [WordPress Trac] #64671: Expand visual regression testing tooling and admin page coverage

[WordPress Trac]

#64671: Expand visual regression testing tooling and admin page coverage
------------------------------+-----------------------------
 Reporter:  JoeFusco          |      Owner:  (none)
     Type:  enhancement       |     Status:  new
 Priority:  normal            |  Milestone:  Awaiting Review
Component:  Build/Test Tools  |    Version:
 Severity:  normal            |   Keywords:  has-patch
  Focuses:  ui, tests         |
------------------------------+-----------------------------
 Visual regression tests catch unintended CSS side-effects across the
 admin. This ticket expands the existing visual regression testing
 infrastructure.

 == Comparison Tooling ==

 * `npm run test:visual` — Generate baseline snapshots.
 * `npm run test:visual:compare` — Diff your branch against trunk
 baselines.
 * `--skip-baselines` — Reuse existing baselines.
 * '''Impact summary reporter''' — Shows changed/unchanged pages after each
 run.

 == Expanded Coverage (22 → 32 pages) ==

 Adds Dashboard, Themes, General/Writing/Permalink Settings, Add New Post,
 Edit Post, Site Health, Updates, and Login.

 == Playwright Best Practices ==

 * Deterministic captures — `animations: 'disabled'`, `fullPage: true`,
 `document.fonts.ready` wait before every screenshot.
 * Volatile element hiding — `stylePath` CSS hides the footer version
 string, toolbar, and Gutenberg menu item globally.
 * Diff threshold — `maxDiffPixelRatio: 0.01` to catch real regressions
 while tolerating sub-pixel rendering differences.
 * Parallelism — `fullyParallel: true` locally, single-worker on CI for
 stable runs.
 * Auth — dedicated `globalSetup` following the existing e2e pattern.

 == Testing Instructions ==

 {{{
   npm run env:start
   npm run test:visual
   npm run test:visual:compare
 }}}

 The impact summary will list any pages with visual differences. The HTML
 report opens automatically for local runs.

 == Motivation ==

 Originally motivated by #64308, but useful for any future admin CSS work.

 == Pull Request ==

 https://github.com/WordPress/wordpress-develop/pull/10914

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/64671>
WordPress Trac <https://core.trac.wordpress.org/>
WordPress publishing platform