feat: allow to use workerIdleMemoryLimit with only 1 worker or runInBand option

[ghusse]

Summary

The option workerIdleMemoryLimit introduced with jest@29 allows to kill workers and respawn new ones when a predefined amount of heap memory is used. This has been introduced as a work-around for this issue.

The problem with this work-around, is that this option has only an effect when tests are run with multiple workers. When test are run on only one runner, they are executed on the main thread and thus this option cannot be applied.

This PR allows to use an unique worker when workerIdleMemoryLimit is set, instead of using the main thread. This allows this option to be used to respawn workers during tests.

This will allow us to run tests both

• in band (necessary for some integration tests that we are running)
• with an applied workerIdleMemoryLimit that will respawn new workers after a given amount of memory usage

Test plan

Example:

node \
       --max-old-space-size=4096 \
       --no-compilation-cache \
       --expose-gc \
      ./node_modules/jest/bin/jest.js \
       --colors \
       --logHeapUsage \
       --verbose \
       --maxWorkers=1 \
       --workerIdleMemoryLimit='500MB' \
       --modulePathIgnorePatterns=.unit.test.[jt]s \
       '--testMatch=**/routes/**/[i-l]*.test.[jt]s' \
       --coverage \
       --coverageDirectory=.nyc_output/jest/routes2

We can see in the logs that the memory usage follows the desired pattern:

 PASS  XXXXXX.test.js (17.017 s, 310 MB heap size)

 PASS  XXXXXX.test.js (7.448 s, 464 MB heap size)

 PASS  XXXXXX/jobs.test.js (127.226 s, 288 MB heap size)

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[ghusse]

Is there something to do on my side to be able to run the CI on this PR?

[SimenB]

triggered ci now

[SimenB]

makes sense to me 👍

[SimenB]

https://github.com/facebook/jest/releases/tag/v29.4.3

[ghusse]

Thanks for the release!

[phawxby]

This a solution to #13171 and #13168. The only thing I wonder is whether this should've included some kind of warnings, for example setting workerIdleMemoryLimit with detectOpenHandles is mutually exclusive. It could potentially be confusing if by the act of trying to diagnose one issue a memory leak is introduced.

https://github.com/facebook/jest/pull/13171/files#diff-3b6e27368c60135ff6a952613123509726d7957e105e605e6deb4c3315ec8984R26-R30

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