test: run unit tests on warpdom instead of jsdom

[sonukapoor]

Pull Request

What

Runs the Jest unit tests (test:cover) and the build tests (test:build) on warpdom instead of jsdom. warpdom is a DOM implementation for unit tests that I maintain; it is written from the WHATWG specifications with the goal that every test gets the same result as on jsdom, only faster. This is a proposal: happy to adjust it or close it if it is not wanted.

Why

The unit tests run about 1.6x faster, with every test keeping its result.

On a GitHub-hosted Ubuntu runner, 2 workers, one warm-up and 5 timed rounds alternating jsdom and warpdom, at master (2026-10-16):

	jsdom	warpdom
Unit tests	8.2 s	5.0 s
Speedup		1.64x (rounds 1.59-1.69x)
Tests with a different status		0

Locally (Apple M4 Pro, Node 22.23, --maxWorkers=2), on this branch and on its parent commit with jsdom, compared test by test with Jest's --json output:

	jsdom	warpdom
Unit tests (jest --coverage)	1,110 passed, 92 suites	1,110 passed, 92 suites
Build tests (other/misc-tests)	8 passed	8 passed
SSR test (Node, unchanged)	1 passed	1 passed
Tests with a different status		0
Unit tests, Jest's time	7.6 s	5.1 s

Coverage stays at 100%; the thresholds pass on both. One local run each, so the local times are indicative only.

How

testEnvironment: 'warpdom' replaces the jsdom environment that kcd-scripts/jest picks for React projects, and the jsdom in other/misc-tests/jest.config.js. jest-environment-warpdom lets Jest find warpdom by that name.

Changes

• jest.config.js: testEnvironment: 'warpdom'.
• other/misc-tests/jest.config.js: testEnvironment: 'warpdom' instead of 'jsdom'.
• other/ssr/jest.config.js: the comment says the other tests run with a DOM (warpdom); the SSR test stays on Node.
• package.json: warpdom (^0.1.3) and jest-environment-warpdom (^0.1.0) as dev dependencies. Both are MIT licensed; their only new dependencies are parse5 8 and @rgrove/parse-xml 5.

No test changes. downshift has no direct jsdom dependency to remove: jsdom 20 stays installed through kcd-scripts, which depends on jest-environment-jsdom 29; nothing loads it after this change.

To reproduce the comparison on master, after npm install:

npx warpdom compare --rounds 3 --workers 2

It runs the suite on jsdom and on warpdom, alternating, and writes .warpdom-compare/report.md with every test whose status changes and the speedup. It uses a temporary wrapper config and changes no files. Or check out this branch and run npm run test:cover and npm run build-and-test.

Caveats:

• warpdom is pre-1.0 (0.1.3) and has far less mileage than jsdom. It is tested against 25 open-source test suites and the Web Platform Tests.
• It differs from jsdom on purpose in a few places: Differences from jsdom. None of them changed a downshift test.
• Like jsdom, it has no layout; the Playwright tests still cover scrolling and focus in a real browser.
• warpdom declares Node.js 22.12 or later. The CI matrix includes Node 20, where npm prints an engine warning for it; the unit and build tests also pass on Node 20.20.2 locally. Happy to drop Node 20 from the matrix instead, if you prefer.

Checklist

• Documentation N/A
• Tests
• TypeScript Types N/A
• Ready to be merged (a proposal; happy to adjust)

Happy to close this if it's not wanted.