* Move unit tests to one folder
* Migrate unit tests to TypeScript
* add test types to lint
* Ensure ts(x) tests are run with util
* Add tsx extension to jest config
* bump
This updates our `jest` configuration to no longer use `babel-jest` and instead uses `@swc/jest` which is much faster. This also updates to the latest version of `jest`, fixes our `tsconfig.json` used for tests (previously types in `node_modules` weren't resolved correctly), and ensures `next/dist` isn't un-necessarily transpiled in `jest`.
Timings for `yarn testheadless test/unit/` on CI
- before: 3m 30s - 4m ([example run](https://github.com/vercel/next.js/runs/3394701995))
- after: under 1m ([example run](https://github.com/vercel/next.js/pull/28400/checks?check_run_id=3395161621))
Timings for `yarn testheadless test/unit/` locally on m1 mac
- before: 90.16 seconds
- after: 29.92 seconds
This PR upgrades `jest-worker` and `jest-cli` to the latest pre-release version, also removed `jest-circus` which is included in Jest by default. `jest-worker@next` includes a fix for memory leak that we need (https://github.com/facebook/jest/pull/11187).
Fixes#22925. This will also improve the OOM issue for `next dev` #15855.
Update tests to setup webdriver stuff in `jest-environment` and re-use one browser session instead of spawning one for each webdriver call to prevent creating too many BrowserStack sessions.
- [x] Move jest config from npm scripts to `jest.config.js`
- [x] Remove obsolete cross-env package (we don't need it anymore 🎉)
- [x] Fix bug where tests are not waiting for webdriver to be ready.
