An Introductory Guide to Visual Regression Testing

Find Waldo in the crowd
Introduction to Visual Regression Testing

The most daunting question that awaits even the most experienced developers right before they push software to production is usually: “did what we changed break anything else?” And with so many things to check and so much at stake, it’s only fair to be concerned about that. Because even the slightest alteration in a single line of code can cripple the functionality of an existing code structure that used to work just fine or cause visual bugs to sneak into production unexpectedly. And when that happens, the user experience (UX) of your application can get ruined in mere seconds. To avoid such unfortunate and unforeseen problems, you need to run continuous tests at the end of every system modification. And to properly do that, the test we suggest is none other than visual regression.

Visual regression testing is done to verify that each UI (user interface) element looks as intended even after we make any changes or updates in the code script. It mainly focuses on the visual aspects of your software, making sure that the UI itself appears correctly to the end-user. Being quite easy to run and quick to catch bugs, visual regression testing is surely a must-have in your quality assurance process. But before we dig any deeper on what visual regression is and all of its advantages, let us show you a few examples of what these notorious visual bugs look like and stress the importance of detecting them in the early stages of the development lifecycle.

How Visual Bugs Affect the User Experience

The visual interface of your web application is the face of your brand. It’s the first thing potential customers see, therefore, giving you the perfect opportunity to make a good first impression. But what if your app is riddled with errors everywhere your users look? What if a graphic is exceeding the expected bounds of the page or an article title is overlapping some images? What if your page contains misaligned texts or partially visible elements?

Visual bugs like these can damage the image of your brand and tarnish your reputation for sure. But the worst part is that such errors are not only detrimental to the design of your software’s visual interface, but they can also impair the functionality of your key features, directly impacting the UX.

Let’s say your end-user is repeatedly trying to click on a button, but can’t because a text is overlapping it. Chances are this user will get frustrated and leave your app never to come back again. Having debilitating effects on the usability of your application, UI bugs cause you to lose customer trust and impede your growth dramatically. However, being highly capable of resolving visual bugs right then and there, visual regression testing can finally save you from such consequences.

So, without further ado, let’s delve into what we mean by visual regression testing and how it works.


What Exactly Visual Regression Means

To put it simply, visual regression testing aims to ensure that each UI element appears in the right color shade, position, or size and that no component overlaps or hides one another. It makes sure that your application is completely defect-free even after various software modifications.

To achieve this, it captures a screenshot of your web application as a baseline image before it’s undergone any changes and takes another screenshot after a code has been altered. If the screenshot comparison doesn’t display any unexpected discrepancies and the new state of your software is identical to your existing reference image, then the test is a success.

But even a highly beneficial software testing method like visual regression comes with its own set of drawbacks when not done right. And, if you choose to perform visual regression tests manually instead of automating your testing process, you will not only miss out on the chance to take advantage of its full potential to create an efficient development lifecycle, but also experience many disadvantages along the way. “What are these disadvantages?” you may ask. Well then, without any further delay, let us run through the list!

Disadvantages of Manual Visual Testing

1. Requires Repetition

Visual regression is not a one-time deal. It needs to take place at the end of every development iteration. Whenever you add new functionality to your software, fix a bug, or alter even a single line of code, you have to check and verify that nothing is regressing before continuing to the next step of production.

As an excessively repetitive process, manual regression testing not only takes too long to execute but also takes up the precious time that you could have spent on more complex and fulfilling projects instead of tedious tasks. Taking all things into account, we think it’s safe to say that manual testing can tremendously slow down your release cycle and have crippling effects on the productivity of you and your team.

2. Prone to Human Errors

No matter how much attention you pay, it’s always possible to overlook some UI errors or even introduce more visual bugs to your software while trying to fix only one. At the end of the day, we’re all human, and we make mistakes. We might write a faulty test script that could corrupt the rest of the application. Or we might fail to notice the difference between the previous and the modified state of our app since these differences can be too subtle for the human eye to catch. So, manually executed tests may be brittle to changes in the UI and less reliable since test results might not be accurate at all times due to human errors.

3. Too Many Testing Environments

Due to the wide range of browsers, devices, screen resolutions, and operating systems that applications are expected to run on, visual regression testing has become incredibly difficult to handle in recent years. And if your app or website has a responsive design, it gets even harder since you now have to deal with visual compatibility issues in addition to an unmanageable number of execution environments.

But the worst part is, even if you don’t touch a single line of code, there are still third-party upgrades you must factor in. And we mean by that is, if a browser suddenly gets updated, it can introduce a bug into your site or application in the blink of an eye. And to detect and eliminate these errors before they make their way into your system, you should constantly be on guard against abrupt changes and continuously run tests in all of these environments, which is quite impossible to manage manually.

Advantages of Automated Visual Testing

Now that you have a clear understanding of all the drawbacks of executing visual testing manually, let’s concentrate on the benefits of performing it automatically.

First things first, since you have to run regression tests after each release of a new product or its updated version and repeat this process every time you alter a code, the regression testing suite is the first in line for automation. By automating it, you accelerate the test execution process of your software and shorten the release cycle of your development all at once.

Another asset to bear in mind is the precision of visual inspection that automation provides. Thanks to the diligent difference detection capability of machine vision, automated visual tests can detect the slightest changes and bugs that get past even the most advanced QA engineers. And when a project grows in scope and becomes even more complex, the odds of them spotting these bugs and differences get even slimmer.

However, automation does not pose a risk to anyone as its role is not to replace humans but, on the contrary, to reduce human efforts. It’s designed to assist developers and testers to achieve maximum efficiency by helping them detect UI bugs earlier in the development lifecycle and conducting tests across multiple environments and screen sizes. Alleviating the load on developers and QA engineers, automated visual tests let them put their time to better use and concentrate on mission-critical tasks that require their knowledge and talent.

But how does automated visual regression testing work? Let’s take a quick look!

How Automated Visual Regression Testing Works

Spotting Waldo in a crowd is like spotting a visual defect in a web app

To make our point stand out, we’ve decided to explain how automated visual regression testing works with the help of someone that many of us are familiar with. That someone is none other than our old friend Waldo, who’s always been too hard to find among a crowd. But what does Waldo have to do with automated visual regression testing? Hear us out!

Let's assume Waldo is a bug in your software

Let’s say Waldo is a visual bug that you don’t want to appear on your application’s page. Yet, somehow, he snuck into your software, nowhere to be seen. He’s out there somewhere, perhaps hiding behind another UI element, causing it to break and corrupt the way it should look or even function. With automated visual tests, you no longer have to break a sweat to spot a visual error, even if it’s as hard as finding Waldo. “How,” you wonder? Here’s a step-by-step explanation of an automated visual testing workflow:

  • The testing tool takes a screenshot of your existing page as a baseline image and then takes another one after any system modifications have been done.
  • To make sure what has changed doesn’t impact any other page or component that’s not meant to be affected, it then compares these two screenshots to see if there’s any difference by highlighting the pixel variations between them. And that is exactly how we spotted Waldo so easily!
Waldo is spotted by Preflight's Visual Assertion
  • After the test comparison, the tool generates a detailed report, showing the discrepancy between the previous and the new state of your application. Based on this report, you then have to decide if the change it displays is an intended alteration or an unexpected visual bug.
  • Once you examine the report and approve of the current screenshot, you can use it as your new and improved baseline image for subsequent test runs.

As you can see, automated visual tests speed up and ease your workflow substantially. However, even though automation is a significant enhancement compared to manual visual testing, we believe that it can be improved even further. And that’s why we developed Preflight. Without further ado, let us tell you what Preflight is and how we’ve made the great method of automation even greater!

Why You Should Automate with Preflight

Even when you automate your visual regression testing process, you still need to manually write a test script to be able to run it first. And no matter how much you enjoy or excel at writing test codes, it can eventually turn into a cumbersome task to carry out due to the repetitive nature of this process. But with Preflight, you don’t even have to write a single line of code. Let us tell you why!

Preflight is a no-code testing tool, meaning anyone can use it. With no requirement to have any technical background or coding knowledge, it allows even the most technologically-challenged people to conduct tests and check the functionality and the visual experience of their web applications. But even if you know how to code, Preflight’s fully automated no-code-driven tests come in quite handy whenever you have trouble dealing with huge test scripts that take too long to execute.

Unlike conventional testing tools, Preflight’s tests are quick to create and easy to run. All you need to do is install it as an extension and run the test on your product, which Preflight will immediately start recording. Preflight’s recorder captures each step of your visual regression test, making it way easier and faster to re-run it if need be.

Similarly, running the test itself is pretty effortless too. By performing a quick drag-and-drop action, you can instantly create a visual checkpoint on any component you want to test. This checkpoint, aka assertion, checks if anything has changed visually after a code modification has taken place by comparing the screenshots of your application’s previous and current states.

To achieve the best result, these visual checkpoints should be compared based on the same screen sizes to minimize and eliminate false positives. Thankfully, Preflight detects what type of baseline it should use for the specific screen size, saving you from the tedious task of setting it up yourself and from dealing with visual compatibility issues.

Capable of offering all these and even more, Preflight is dedicated to keeping your web applications visually and functionally flawless, providing your valuable users with the smooth experiences they deserve.

Key Takeaways Visual regression testing offers an elaborate set of advantages. First and foremost, it protects your brand’s integrity by detecting visual bugs in the early stages of your development lifecycle, or in other words, before it’s too late. It also provides your visitors with consistent and seamless user experiences, discouraging them from slipping away. This way, it plays a remarkable role in the maximization of your user conversion and retention rates. Yet, last but not least, visual regression testing – especially when automated – makes life way easier for developers and QA engineers. By executing tests a lot smoother, visual regression lightens the load on those who have to constantly write codes and conduct tests.

If you too would like to render your web application correctly and bug-free on multiple browsers and screen sizes with ease and speed, look no further than Preflight. Head over to our website to find out all you need to know and explore our advanced features, products, and services. And if you’re one of those people who needs to take something for a test drive before they commit to it, don’t hesitate to try Preflight for free. And don’t forget: with Preflight, anyone can be a skilled tester!