Allow specifying --runInBand in config file

[felipeochoa]

🚀 Feature Proposal

Add an option to the file-based config equivalent to setting --runInBand on the CLI

Motivation

For node projects that have external dependencies (e.g., sqlite, filesystem, shared libs) that can't (easily) be made safe to access in parallel, it would be nice to always force jest to run sequentially.

Example

// jest.config.js
module.exports = {
  runInBand: true,
}

Pitch

The main alternative solution would be to add the flag to a package script (e.g., "test": "jest --runInBand"). This requires configuring all editor plugins (like this one) which duplicates these settings and makes it harder to have node and broweser packages together. In my own setup, it's easier to always run jest with --runInBand, but that's unnecessarily slow many times.

[tokland]

Related: #3215

[felipeochoa]

Woops didn't find that originally, thanks

[rickhanlonii]

Closing as a dupe of #3215 👌

[github-actions]

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