Vue.js 2 and Bootstrap 4 Web Development

Getting started with Jest

Let's start by testing a small sum function and check that it correctly sums two numbers.

The first step would be, of course, to install Jest:

npm install jest

Create a directory test and add a file called sum.js with the following content:

// test/sum.js
export default function sum (a, b) {
  return a + b
}

Now add a test spec file for this function:

// sum.spec.js
import sum from './sum'

describe('sum', () => {
  it('create sum of 2 numbers', () => {
    expect(sum(15, 8)).toBe(23)
  })
})

We need a command to run tests. Add an entry "test" to the package.json file that will call a command jest:

// package.json
"scripts": {
  //...
  "test": "jest"
}

Now if you run npm test, you will see some errors:

Errors in the test output with when ...