Replace Jest with Vitest

[ovidiuch]

This is an experiment, not sure how it will go.

• Remove jsdom default env and enable it on a test by test cases (or by folder).
• Remove CJS mocks that were needed for Jest.
• Try Vitest 1.0.0-beta.
• Try VS Code integration.

Problems

• Unclear: Vitest/Vite does't import modules without extension? This creates some errors with package entry points and resolving paths when building webpack configs. Potentially relevant: Importing a .js typescript resource from a typescript file fails vitejs/vite#3040 (comment).
• Sync require() doesn't work in Vitest for the getFixtures test.

Current status

• Update: Vitest 1.0.0 has been releaased, try it out: https://github.com/vitest-dev/vitest/releases/tag/v1.0.0.

2023-12-02

After running into a bunch of issues I'm pausing this PR for now. On one hand, most of the repo was easy to migrate to Vitest and running native ESM in tests is a great improvements–I can remove the cjsMocks folder and upgrade all Node dependencies that have recently upgraded to pure ESM. On the other hand, there are some blockers at the moment:

• getFixtures works with sync require() and I don't know if it can be made to run in Vitest. I might refactor this API altogether and afterwards this problem will solve itself. But the refactor isn't trivial because we need a way to call it and generate test cases dynamically based on the returned fixture items. Last time I checked you couldn't asynchronously generate test cases (at least in Jest).
• Surprisingly, the entire Cosmos test suite runs quicker in Jest. Not a deal breaker but something to consider.
• The packages/react-cosmos/src/devServer/__tests__/startDevServer.ts test fails on Windows in Vitest (in GitHub Actions). I haven't tried in on a Windows machine yet, and it's hard to debug in GitHub actions. But weirdly if I run the test individually (just the failing test case or the entire test file, or even the entire package) they pass. It's only when I run the entire mono repo test suite that it fails. It's not obvious why and I'm wondering if Vitest is stable at this point.
  • Update: Ran the whole test suite after a few days and it passed on Windows, but timed out on Ubuntu 🤦‍♂️.
• Another weird thing is I've been trying to disable threads to see if that'll fix the previous problem (or the one before related to speed) and I just don't know how. The documentation mentions the --no-threads CLI arg but when I try it the CLI fails with a CACError: Unknown option --threads exception.
• I think I'll wait until Vitest 1.0 is out of beta and try again.

[cloudflare-pages]

Deploying with    Cloudflare Pages

Latest commit:	f2b8590
Status:	✅  Deploy successful!
Preview URL:	https://227f6c65.reactcosmos.pages.dev
Branch Preview URL:	https://vitest.reactcosmos.pages.dev

View logs