If you’re peripherally familiar with aspects of software development, you might have heard of visual regression testing. This is a specific subset of regression testing which is key to ensuring that when updates are made to the underlying code, no other issues have been caused elsewhere by these changes.

Let’s go into a little more detail about the specifics of visual regression testing, including how it is achieved and what it involves, so you understand why it is necessary for projects of all sizes.

The basics

In simple terms, visual regression testing applies regression testing practices solely to the visual elements of the program in question.

If any under-the-hood tinkering takes place, developers obviously want to ensure that this doesn’t break the user interface (UI), or cause it to behave in unintended ways.

The processes

Visual regression testing can be carried out manually, although today it is more common for visual regression testing tools to be put to work, automating aspects of the process and improving the accuracy as well as the repeatability of the steps involved.

So how do testers know what, if anything has changed? Well, usually they will compare screenshots of the software’s UI before the changes to the code were made, with how it looks afterwards.

In some cases the differences will be stark, in others subtle. Whatever the case, if new code has had unintended consequences, it will likely need further investigation.

The examples

A common example of the type of UI issue that can be identified with visual regression testing involves changes in the size and orientation of onscreen interface elements.

Say that in the new version of the software, users are less able to see menu items because they are overlapped by an image or another component of the UI.

This would sour the experience of using it, and in the case that the package is designed to attract external users, it could cripple its chances of succeeding on the open market. For custom software designed for internal use, productivity would suffer in this scenario.

The variability

Another important aspect of visual regression testing is that it takes into account the wide variety of device types that developers have to accommodate in their software coding efforts at the moment.

Code changes might result in no UI issues on desktop PCs, but could leave things looking like an incoherent mess on portable devices like smartphones, for example. The only way to know if this is the case is to test for as many different scenarios as possible, and find solutions to any problems that rear their heads.

Another variable that must be encompassed by testers is the different user behaviors that any software package will experience when it is out in the wild. Certain visual bugs might only ever crop up if a user follows a specific sequence of interactions or events, and so researching these and replicating them within the testing is part and parcel of covering all the bases.

The hybrid approach

Earlier we mentioned that certain aspects of visual regression testing can be carried out automatically, while others are achievable manually. The reality is that most testing involves a combination of software tools and human testers in order to get the best possible outcome.

Baselines are measured before changes are made, and then comparisons of visual elements can be completed with control images acting as the basis for identifying differences or outright bugs.

Professional testers are presented with the results, and can use their own expertise to pinpoint problems and begin the process of suggesting options for troubleshooting. In this sense, testers once again work hand in hand with developers to deliver a better end product.