jest-environment-linkedom

1. What is this

This will help run Jest tests in the linkedom environment, based on https://jestjs.io/docs/next/configuration#testenvironment-string. Example of a working basic project: https://github.com/mikemadest/example-linkedom. This is an experiment to see what I can get working, WIP.

2. Why the hell

After taking an interest in Linkedom (https://github.com/WebReflection/linkedom) I came upon this discussion and used Stephen Harberman code as starting point (this code).

The goal was just to make basic tests pass.

3. I wanna play too

3.1 Add those dependencies to your package.json:

    "linkedom": "^0.11.0",
    "jest-fake-timers": "^1.0.2",
    "jest-mock": "^27.0.6",
    "jest-util": "^27.0.6",

3.2 After copying the files in a linkedom folder, update jest.config.js to whatever your path is to this file:

module.exports = {
  // ... you other configs ...
  testEnvironment: './linkedom/jest-environment-linkedom.js',
};

You can also update your package.json like:

  "scripts": {
    "test": "react-scripts test  --env=./jest-config/jest-environment-linkedom.js --watchAll=false",
  },

4. Basic test example (jest + react testing library):

import React from 'react';
import {
  cleanup,
  screen,
  render,
  fireEvent,
} from '@testing-library/react/pure';

describe('Basic test', () => {
  const mockedHandleClick = jest.fn().mockImplementation(() => {
    console.log('test click');
  });

  beforeAll(() => {
    render(
      <div>
        <p>test</p>
        <p className="searchNode">search</p>
        <button type="button" onClick={mockedHandleClick}>
          click me!
        </button>
      </div>,
    );
  });

  afterAll(cleanup);

  it('should render and find content', () => {
    expect(screen.getByText(/search/i)).toBeInTheDocument();
    expect(screen.queryByText('blah')).not.toBeInTheDocument();
    expect(
      screen.getByRole('button', { name: 'click me!' }),
    ).toBeInTheDocument();
  });

  it('should click the button', () => {
    fireEvent.click(screen.getByRole('button', { name: 'click me!' }));
    expect(mockedHandleClick).toHaveBeenCalled();
  });
});

5. What was done

• Added window.location to avoid crash

• Axe test require NamedNodeMap which was undefined. Very crude "fix" just to avoid the crash (JSDOM as a full implementation but for now I'm skipping that)

• testing library toBeInTheDocument (and probably other methods) uses getRootNode which was undefined, added a "polyfill"

• Missing getComputedStyle, reported here too: https://githubmemory.com/repo/WebReflection/linkedom/issues/53 So I added a "polyfill" which mostly avoid errors for now

• extends jest-env-node to avoid reinventing the wheel and avoid setting global.RegExp as this is breaks instanceof.

More on that last one:

Problem is that Object in VM context are different distinct objects. References for that issue: https://github.com/jsdom/jsdom/compare/7.0.1...7.0.2 where jsdom avoided adding Date and RegExp to "this" for the same reason.

Jest globals differ from Node globals: jestjs/jest#2549

vm instanceof operator don't work as expected: nodejs/node-v0.x-archive#1277

6. Status

• render and content checking pass.
• RegExp are now working
• onClick test fail: work in progress for a pull request to implement event bubbling in linkedom