Jest spends several seconds in `loadTSConfigFile` before running tests

[jtbandes]

🐛 Bug Report

I am working in a yarn 2 monorepo that has a handful of separate TypeScript packages. When running Jest on a small test file, it takes about 8 seconds before the test even starts running. During this time it seems like Jest is running loadTSConfigFile and processing all the tsconfig files in our repo:

To help address I created a custom tsconfig for jest, but needed to keep some of the typeRoots. This helped somewhat but the performance is still quite poor. I'd appreciate any advice on how to speed things up! Why does it take so long for jest to process these config files? Should I convert them all to jest.config.json instead of jest.config.ts?

To Reproduce

Steps to reproduce the behavior:

• Check out this repo @ 2a41078a and run yarn.
• Run yarn test app/util/time.test.ts. Or yarn test:debug app/util/time.test.ts to inspect with Chrome dev tools.

Expected behavior

The test file is small, so it should run quickly.

Link to repl or repo (highly encouraged)

https://github.com/foxglove/studio/tree/2a41078ac99f3a636e4288c31bb188e54a9f2ed3

envinfo

  System:
    OS: macOS 11.2.3
    CPU: (8) arm64 Apple M1
  Binaries:
    Node: 15.9.0 - ~/.nvm/versions/node/v15.9.0/bin/node
    Yarn: 2.4.1 - ~/.nvm/versions/node/v15.9.0/bin/yarn
    npm: 7.5.4 - ~/.nvm/versions/node/v15.9.0/bin/npm
  npmPackages:
    jest: 27.0.0-next.8 => 27.0.0-next.8 

[jtbandes]

It seems like converting all jest.config.ts files to jest.config.json helps a lot. Still think this performance issue is an important one to flag.

[SimenB]

Seems like ts-node is slow, not much we can do about that here. You could use a JS file and jsdoc comments instead of a TS file and skip the compile (drawback is that it won't fail on startup, but you'll at least get red squiggles in you IDE). See example in #11110.

We could of course include some note that it'll be slower to spin up the TS compiler than not, but not sure where it'd fit? Possibly by the samples added in #11110?

[cspotcode]

transpileOnly will also make it waaay faster. https://typestrong.org/ts-node/docs/performance

If you really want ts-node to be typechecking your config, you can use some of the other advice on that page. But transpileOnly is my recommendation.

[gbiryukov]

indeed, it will help a lot if jest will load ts config files with transpileOnly: true option by default

[github-actions]

This issue is stale because it has been open for 1 year with no activity. Remove stale label or comment or this will be closed in 30 days.

[jtbandes]

Sounds like this is still an issue.

[github-actions]

This issue is stale because it has been open for 1 year with no activity. Remove stale label or comment or this will be closed in 30 days.