In this chapter:
- Replicating a browser’s JavaScript environment in your tests
- Asserting on DOM elements
- Handling and testing events
- Writing tests involving browser APIs
- Handling HTTP requests and WebSocket connections
Trying to write a client-side application without using JavaScript is as difficult as baking a dessert without carbohydrates. JavaScript was born to conquer the web, and in browsers, it has shone.
In this chapter, we’ll cover the fundamentals of testing front-end applications. Together, we’ll build a small web client for the back-end we’ve written in Chapter 4, and learn how to test it.
During the process of building and testing this application, I’ll explain the peculiarities of running JavaScript within a browser, and, because Jest can’t run in a browser, I’ll teach you how to simulate that environment within Node. Without being able to emulate a browser’s environment in Jest, you wouldn’t be able to use it to test your front-end applications.
When testing front-end applications, assertions can become more challenging, because now you’re not only dealing with a function’s return value, but also with its interaction with the DOM. Therefore, you will learn how to find elements within your tests, and perform assertions on their contents.