Frontend Architecture for Design Systems

Chapter 14. Red Hat Testing

Visual Regression in Action

PhantomCSS has been my go-to tool for the past few years because it provides component-based comparison, with a headless browser and scripting library that can be integrated with my current build tools. So let me walk you through the setup of PhantomCSS and how we are currently using it at Red Hat.

The Testing Tools

PhantomCSS is a powerful combination of three different tools:

• PhantomJS is a headless WebKit browser that allows you to quickly render web pages, and most importantly, take screenshots of them.
• CasperJS is a navigation and scripting tool that allows you to interact with the page rendered by PhantomJS. We are able to move the mouse, perform clicks, enter text into fields, and even perform JavaScript functions directly in the DOM.
• ResembleJS is a comparison engine that can compare two images and determine if there are any pixel differences between them.

We also wanted to automate the entire process, so we pulled PhantomCSS into Grunt and set up a few custom Grunt commands to test all, or just part, of our test suite.

Setting Up Grunt

Now before you run off and download the first Grunt PhantomCSS you find on Google, I’ll have to warn you that it is awfully stale. Sadly, someone grabbed the prime namespace and then just totally disappeared. This has led to a few people taking it upon themselves to continue on with the codebase, merging in existing pull requests and keeping things current. One of the better ...