We need a way to limit to execute tests in a single file concurrently without swamping the CPU

🚀 Feature Proposal

test.concurrent needs some kind or limit to its concurrency to prevent it swamping the CPU. – or – Something like test.farm which feeds the tests into a worker farm rather than immediately executing them.

Motivation

I use puppeteer with jest-image-snapshot to perform visual regression testing. I use globby to gather a list of output html files and feed them into test(), I’d like to feed them into test.concurrent() but that then tries to open 200 tabs at the same time then things go wrong very quickly.

Example

I’m thinking this should probably be the default operation of the feature, much like the maxWorkers option. If people are confident their code will behave fully concurrently then perhaps expose a maxConcurrentWorkers option. – or – test.farm(‘test name’, async() => { // Some big horrible test });

Pitch

test.concurrent is a core feature, it makes sense for it to be addressed here.

[dangreenisrael]

In case someone comes across this looking to limit concurrency: https://jestjs.io/docs/en/cli#maxconcurrency-num

[kevlened]

If you’re willing to split your test.concurrent into different files, I wrote a concurrent test runner. Instead of the default of running each file in a different process, it runs them concurrently. You can control the concurrency with maxConcurrentTests.