Testing in JavaScript

Testing is usually done at a library level if you make a custom library for example named sum.js the best way to manage your test would be to put them into a sum.text.js file. This method of storing your tests removes the testing part of your application from the rest of it and makes sure none of the tests get bundled and sent to the client.

Installing Jest

bash
npm install --save-dev jest

javascript
test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

This is a test for a function that adds two numbers called sum. We first define the test inside of the test function. The first argument is the text that displays when the function passes the test. The next argument is the function to run during the test, inside this function we use the Jest syntax to configure the test. expect is the main function where we put the sum function with test parameters. Then off of that function, we are expecting the sum function when giving the parameters 1 and 2 to be 3. All of Jest's testing criteria are written this way making the experience super easy to get started with.

To get a full list of all of the matches visit the jest docs here

javascript
"scripts": {
   "test": "echo \"Error: no test specified\" && exit 1"
 },

javascript
"scripts": {
   "test": "jest"
 },

To run the tests run npm test in a terminal and the output will look something like this: