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Using Jasmine to Unit Test Your JavaScript App

Test Promises Using Async and Await

Learn to test Promises using async and await.

We'll cover the following...

In everyday work, we often need to deal with Promises (MDN article). Jasmine allows for a straightforward way of testing these using async and await (MDN article)

The ArticleDelete class

What follows is a very simplified example of a class that handles deleting articles in a browser application. It accepts some input and makes a request to a server API if conditions are met.

For this lesson, the ArticleAPI methods are considered returning instances of Promise. So, the delete method returns a Promise.

Run the code playground below and see the breakdown below.

const specReporter = require('jasmine-spec-reporter').SpecReporter

module.exports = {
  srcDir: "src",
  srcFiles: [
    "**/*.?(m)js"
  ],
  specDir: "spec",
  specFiles: [
    "**/*[sS]pec.?(m)js"
  ],
  helpers: [
    "helpers/**/*.?(m)js"
  ],
  random: false,
  stopSpecOnExpectationFailure: false,
  browser: {
    name: "headlessChrome"
  },
  reporters: [new specReporter()]
}
Unit testing a Promise example

ArticleDelete class breakdown

The ArticleDelete class is relying on the ArticleAPI class to make a DELETE /api/article/:id call if conditions are met.

  • ArticleAPI is a class that would implement the server API call. It’s empty above because that’s outside of the current lesson scope, and we’ll be mocking its responses for the tests.

  • ArticleDelete is the main class. Its breakdown is below:

    • import { ArticleAPI } from './article-api.mjs';

      This line imports the ArticleAPI dependency from the adjacent module in the current folder, article-api.mjs.

    • export class ArticleDelete {

      This line declares and exports the class to be used in other modules.

    •   /** @type {ArticleAPI} */
  articleAPI;

  /**
   * @param { ArticleAPI } article the article api
   */
  constructor(articleApi) {
    this.articleAPI = articleApi;
  }

      These lines declare the articleAPI property and populates it when an instance of the class gets constructed. In other ...