Worker from imported NPM module causing jest tests to fail

Question

I installed browser-image-compression which, as part of its functionality, creates a Worker. Now when I run jest tests, I get the following error:

Test suite failed to run

ReferenceError: Worker is not defined

There are no tests connected to the function which uses browser-image-compression.

The scripts section in package.json has the following two lines

"test": "react-scripts test",
"test:ci": "cross-env CI=true react-scripts test"

Oh, and I have a file for setting up tests. Should I mock Worker in here?

import { configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import '@domain/yup';

configure({
  adapter: new Adapter()
});

global.fetch = require('jest-fetch-mock');

Answer 1

Late in responding to this but it could help others - but following this comment helped me with this issue.

If you add the following to its own file - I have mine within the same dir as the setupTests file named workerMock.js:

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

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

Then import that Worker file into your test setup file and add window.Worker = Worker. Your setup file may look like:

import { configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import '@domain/yup';

import Worker from 'path-to-your-worker-file-above';

configure({
  adapter: new Adapter()
});

global.fetch = require('jest-fetch-mock');

window.Worker = Worker;

Hope this helps