Hacktoberfest — get involved in OSS with jest-extended

23 October, 20172 min read
Mount tiede

Want to get involved in open source software but don’t know where to begin? We’ve all been there! Hacktoberfest is a great incentive for people to start contributing back to the OSS community and you can get yourself some free swag 👕. With the clock ticking down on Hacktoberfest — I’ve got a new open source project that you’re more than to contribute to! jest-extended 🎉

Do you use Facebook’s amazing testing library Jest? If you haven’t then I definitely recommend you give it a try — amongst other things the developer experience of using it is second to none.

I recently found a feature of Jest that I thought was very cool!

Extending expect

You can use expect.extend to add your own matchers (assertions) to Jest. For example, let’s say you wanted to check a value is true. You could abstract that into a toBeTrue matcher:

  toBeTrue(given) {
    const pass = given === true;
    if (pass) {
      return {
        message: () => `expected ${given} not to be true`,
        pass: true,
    } else {
      return {
        message: () => `expected ${given} to be true`,
        pass: false,

test('true and false', () => {

This extend API got me thinking that it would be cool to have more specific Jest matchers. So I’ve decided to open source jest-extended as a new project to accomplish this.

In the spirit of Hacktoberfect I have created a series of issues for new matchers that I think would be useful to have as part of jest-extended but you can always raise an issue if you can think of others 🙂. I’ve labelled them with New Matcher, Beginner Friendly and Hacktoberfest.

Feel free to contribute by sending a pull request for any of the issues that aren’t already being worked on, just put a comment on the issue that you would like to work on it so that others don’t too. If you’re new to GitHub and sending pull requests, then I recommend you check out Kent C. Dodds’s egghead course on contributing to open source projects.

Each new matcher should be beginner friendly and I’m more than happy to help out if you get stuck, so no excuses not to get involved 😜. A good place to start is the contributing guide.

I look forward to seeing you over in the repo!

Matt Phillips

Matt Phillips

Open-source software engineer and tech founder with a passion for teaching all things software related, career development and building products.

Don’t miss out on on future posts, projects and products I’m working on by following me over on Twitter @mattphillipsio.