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Jest

Jest allows to write and execute test.

Set up

npm install --save-dev jest

# To use ES6 module import statements:
npm install --save-dev babel-jest @babel/core @babel/preset-env

In package.json:

{
  "scripts": {
    "test": "jest"
  }
}

Create a babel.config.js in the root dir

module.exports = {
  presets: [['@babel/preset-env', {targets: {node: 'current'}}]],
};

Usage

List of expression

Create a .test.js version of the .js file to test.

For example: sum.js -> sum.test.js

In the .test.js file:

import { functionToTest } from './sum.js'

test('Write comment here', () => {
  expect(functionToTest(argument)).toBe('expected result');
});
    
// example:
test('Test if string is capitalize', () => {
  expect(capitalize('Test')).toBe('TEST');
});

Then run npm test