Web Workers in Jest

[thkruz]

for anyone using ESM and creating worker separately in a js file (and using worker-loader to load the worker)
setting window.Worker = Worker is not going to work since here we are importing the worker as a module.
create __mocks__ folder and do a manual mock for your worker module, e.g:

├── src
│   ├── __mocks__
│   │   └── myworker.worker..js
│   └── myworker.worker..js

and in your __mocks__/myworker.worker.js file:

class Worker {
  constructor(stringUrl) {
    this.url = stringUrl;
    this.onmessage = () => {};
  }

  postMessage(msg) {
    this.onmessage(msg);
  }
}

export default Worker;

and don't forget to call jest.mock('myworker.worker.js')

spent a lot time struggling with this!

Originally posted by @kamaladenalhomsi in jestjs/jest#3449 (comment)

[thkruz]

Fixed in ca2f97e