What

Jest's default runner uses a new child_process (also known as a worker) for each test file. Although the max number of workers is configurable, running a lot of them is slow and consumes tons of memory and CPU. jest-runner-concurrent runs your tests concurrently instead of in parallel, so you can run hundreds of tests quickly with only a few workers.

Caveats

To take advantage of the performance gains, your tests:

1. Must be asynchronous
2. Share no state with another test

Install

npm install --save-dev jest-runner-concurrent

Enable

There are a couple ways to enable the runner

package.json

{
  "jest": {
    "runner": "jest-runner-concurrent"
  }
}

jest.config.js

// <project_root>/jest.config.js

module.exports = {
  runner: 'jest-runner-concurrent'
}

Configure

There are also a few ways to configure the runner

Defaults:

• maxConcurrentTests - No max. 0 is the same as no max

package.json

{
  "jest-runner-concurrent": {
    "maxConcurrentTests": 100
  }
}

jest-runner-concurrent.config.js

module.exports = {
  maxConcurrentTests: 100
};

License

MIT