Jest

npm install --save-dev babel-jest babel-preset-env babel-core regenerator-runtime (puese que regenerator-runtime no sea necesario)

package.json

(https://jestjs.io/docs/en/configuration.html)

Pimer nivel:

"jest": { "verbose": true, "testURL": "http://localhost/" }, Esto evita el error 'SecurityError: localStorage is not available for opaque origins'

Dentro de "scripts":

"test": "jest"

"watch": "jest --watchAll *.js" -> Para hot reloading

Hacer un archivo <file_name>.test.js

npm run test

Testear DOM element

• npm install --save-dev jest-dom

import { getById } from './utils'
import 'jest-dom/extend-expect'

it('getById', () => {
    document.body.innerHTML = /*html*/`
    <div class="container" id="input-container"></div>`
    expect(getById('input-container').outerHTML).toBe('<div class="container" id="input-container"></div>')
})