[jest-dev-server] fake timers prevent waitOn to check for liveliness

[dackmin]

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🐛 Bug Report

When using jest's timers: 'fake', waitOn cannot check for the server to be alive because the underlying rxjs timers cannot run properly. When setting timers: 'real', it works perfectly.

To Reproduce

Set timers to 'fake' in your jest config and watch it timing out every time.

Expected behavior

I don't know if there's anything against using fake timers with jest dev server, but that's a thing I heavily rely on in my tests because I deal with a lot of setTimeouts, so I thought this should be considered as a bug.

Link to repl or repo (highly encouraged)

https://replit.com/@dackmin/jest-dev-server-timers

repl cannot run spawnd due to missing ps, but download the project as a zip and just run yarn && yarn test inside.

Run npx envinfo --system --binaries --npmPackages expect-puppeteer,jest-dev-server,jest-environment-puppeteer,jest-puppeteer,spawnd --markdown --clipboard

Paste the results here:

## System:
 - OS: macOS 11.5
 - CPU: (12) x64 Intel(R) Xeon(R) CPU E5-1650 v2 @ 3.50GHz
 - Memory: 4.69 GB / 32.00 GB
 - Shell: 5.8 - /bin/zsh
## Binaries:
 - Node: 16.6.0 - ~/.nvm/versions/node/v16.6.0/bin/node
 - Yarn: 1.22.5 - ~/.yarn/bin/yarn
 - npm: 7.19.1 - ~/.nvm/versions/node/v16.6.0/bin/npm
 - Watchman: 4.9.0 - /usr/local/bin/watchman
## npmPackages:
 - jest-dev-server: 5.0.3 => 5.0.3 

[dackmin]

For anyone passing by, toggling fake/real timers before and after server setup works:

jest.useRealTimers();
await devServer.setup(...);
jest.useFakeTimers();

But I don't know if it's not flex tape on a dam more than a real solution 😄

[gregberge]

The solution provided by @dackmin makes sense.