Visual regression testing tools

Since we first mentioned visual regression testing tools in 2014, the use of the technique has spread and the tools landscape has evolved. BackstopJS remains an excellent choice with new features being added regularly, including support for running inside Docker containers. Loki was featured in our previous Radar. Applitools, CrossBrowserTesting and Percy are SaaS solutions. Another notable mention is Resemble.js, an image diffing library. Although most teams use it indirectly as part of BackstopJS, some of our teams have been using it to analyze and compare images of web pages directly. In general, our experience shows that visual regression tools are less useful in the early stages when the interface goes through significant changes, but they certainly prove their worth as the product matures and the interface stabilizes.

Growing complexity in web applications has increased the awareness that appearance should be tested in addition to functionality. This has given rise to a variety of visual regression testing tools, including CSS Critic, dpxdt, Huxley, PhantomCSS, and Wraith. Techniques range from straightforward assertions of CSS values to actual screenshot comparison. While this is a field still in active development we believe that testing for visual regressions should be added to Continuous Delivery pipelines.