WTF is Jest?

Jest is a JavaScript testing framework.

It's JavaScript, so yeah, there are a whole heck of a lot of frameworks to choose from when it comes to writing tests. Many feel passionate about one over another. But Jest seems to be the more popular choice today.

As a test framework, its job is to provide you with an API that will help you test your program's code. Here's a quick example:

Let's say you have a function called add that is exported from a utils.js file. It adds to numbers together and returns the result. It looks like this:

utils.js

exports.add = function (num1, num2) {
  return num1 + num2;
};

You may have a Jest file right alongside it that loads the function and writes tests for it. A simple test would be to ensure that 1 + 1 = 2. That Jest file might look like this:

__tests__/utils.js

const { add } = require("../utils");

test("1 + 1 = 2", () => {
  expect(add(1, 1)).toEqual(2);
});

This was a super simple example just to give you a preview. To actually put this to action and learn more about Jest, visit its Getting Started guide.