Run test suite in real Chromium via vitest browser mode

[myabc]

Ticket

N/A — follow-up to the selector-scoping work in #4.

What are you trying to accomplish?

Run the test suite in a real browser. happy-dom restricts querySelector combinator matching to the query root's subtree, which is non-spec — real browsers match document-wide and filter results to descendants. That divergence sits exactly on this library's core domain: the :scope anchoring integration tests in #4 passed vacuously (green even with anchoring disabled), and the original scoping leak was invisible to the suite.

What approach did you choose and why?

Vitest browser mode with the Playwright provider, all tests headless in Chromium — not a hybrid split. The library is DOM-first and tiny (60 tests, ~2.4s total), so one runner/one config beats maintaining a unit/browser split; pure-logic tests run fine in the browser too.

• Imports migrated bun:test → vitest (spyOn → vi.spyOn); happy-dom, test/setup.ts, and the bunfig.toml preload deleted.
• New environment guard test asserts spec-correct document-wide combinator matching, so a regression to an emulated DOM is caught immediately.
• CI installs the Playwright Chromium binary (bunx playwright install chromium --with-deps); Bun stays as package manager/runtime.
• CLAUDE.md records the exception to its bun test default.

Proof the migration achieves its goal — mutation canary: with anchorToScope neutered to the identity function, the previously-vacuous anchoring tests now fail (12 failures, including combinators cannot match through ancestors outside the root); reverted after checking. Firefox/WebKit matrix deliberately skipped for now — :scope is baseline everywhere.

No changeset: test infrastructure only, no published behavior change.

Stacked on #4; chain #1 ← #2 ← #4 ← this.

Verification: bun run test 60 pass in Chromium, bun run typecheck clean, bun run build clean.

Merge checklist

• Added/updated tests
• Lookbook docs n/a — npm library
• Tested major browsers — entire suite now runs in real Chromium on every CI push

[Copilot]

Pull request overview

Migrates the project’s test runner from Bun’s bun:test + happy-dom to Vitest browser mode backed by Playwright Chromium, so selector scoping behavior is validated against real browser querySelector semantics.

Changes:

• Adds Vitest browser-mode configuration (Playwright provider) and updates CI to install Chromium and run vitest run.
• Updates all test imports/spies from bun:test to vitest (spyOn → vi.spyOn) and removes happy-dom registration/preload.
• Adds an environment-guard test asserting spec-correct document-wide combinator matching.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
vitest.config.ts	Enables Vitest browser mode with the Playwright provider and Chromium instance.
test/setup.ts	Removes happy-dom global registration (no longer needed under real Chromium).
test/query.test.ts	Migrates test APIs to Vitest and updates commentary to reflect real-browser execution.
test/integration.test.ts	Migrates to Vitest APIs (vi.spyOn).
test/helpers.test.ts	Migrates to Vitest APIs.
test/harness.test.ts	Updates harness check and adds a DOM-semantics environment guard test.
test/element-definition.test.ts	Migrates to Vitest APIs (vi.spyOn).
test/blessing.test.ts	Migrates to Vitest APIs (vi.spyOn).
test/barrel.test.ts	Migrates to Vitest APIs.
package.json	Switches test script to vitest run and adds Vitest browser deps.
CLAUDE.md	Documents the testing exception (Vitest browser mode vs bun test).
bunfig.toml	Removes Bun test preload config.
bun.lock	Updates lockfile for Vitest/Playwright-related dependencies.
.github/workflows/test.yml	Installs Playwright Chromium in CI and runs the new test command.

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[myabc]

🤖 Closing: GitHub's stack feature blocks retargeting this PR's base to main. Replaced by a standalone PR from the same branch, rewritten against main so it can land first.