small helper to facilitate tests with async code

promises.js

/**
 * Small helper that keeps all running promises on a
 * queue and allows a test to wait for all async code
 * to finish before doing any assertions
 */

const NativePromise = window.Promise
let queue = []

class TestPromise extends NativePromise {
  constructor(cb) {
    super(cb)
    queue.push(this)
  }
}


/**
 * Install test promises. Make it possible to
 * wait for all promises by calling `flushPromiseQueue`
 */
export default function install() {
  window.Promise = TestPromise
}

/**
 * Clears the promise queue.
 *
 * @returns {Promise} a promise the resolves only when all promises are finished
 */
export function flushPromiseQueue() {
  const all = NativePromise.all(queue)
  queue = []
  return all
}

/**
 * Restore window.Promise to its initial value
 */
export function restore() {
  queue = []
  window.Promise = NativePromise
}


// now you need to install it in your a setup file somewhere
// e.g setup.js
// beforeEach(() => install())
// afterEach(() => restore())

// and use in a test
// import { flushPromiseQueue } from 'test/promises'
// ...
// flushPromiseQueue().then(() => {
//   asserts here are guaranted to run after all promises are finished
// })