Access the number of workers in globalSetup

[osdiab]

🚀 Feature Proposal

Add an environment variable or otherwise expose to the globalSetup script how many jest workers are being spun up for a test run

Motivation

I want to setup n separate databases to run database tests in parallel while still maintaining isolation from a globalSetup script that happens before all test suites, and then access them based on the JEST_WORKER_ID flag, like described in this article. But unfortunately it doesn't seem like the JEST_WORKERS env var in that article actually exists; I can't find it in my environment nor in the jest source by searching for it here on Github source, issues, PRs.

Example

See the article linked above

Pitch

Jest internally decides the number of workers so it's not straightforward to do this outside of it if I understand correctly

[osdiab]

i worked around this by assuming that maxWorkers is going to be the total number of workers - just realized that that piece of config is passed to the function that the globalSetup module exports. That works for me for now, though would be nice if the actually authoritative number were passed.

[rinogo]

One thing to keep in mind is that maxWorkers "defaults to the number of the cores available on your machine minus one for the main thread".

I was looking for a way to use more workers, but the default setting actually seems like it might be ideal.

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[SimenB]

This is passed as config to the exported function, isn't it?

[alencarandre]

I am using jest version 29.3.1 and I found it

process.env.JEST_WORKER_ID

[d4vidi]

I am using jest version 29.3.1 and I found it

process.env.JEST_WORKER_ID

@alencarandre I think this stands for the unique ID each worker has, rather than the total count.

[SimenB]

Correct, that's something different.

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#6486 made sure to pass globalConfig to the setup files, so you can just inspect that.

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