What is visual regression testing?

by | Sep 25, 2023 | 0 comments

Picture this: You’ve spent countless hours perfecting the aesthetic appeal of your website, carefully aligning every button, image, and text block. Then out of the blue, an unexpected change sends your meticulously designed layout into utter chaos. Panic ensues…

But wait! What if I told you that there is a superhero waiting in the wings that can save you from such design catastrophes? Enter the protagonist of our narrative – Visual Regression Testing.

This unsung hero works tirelessly behind the scenes, making sure your website’s visual elements remain consistent and unblemished amidst a sea of changes.

So buckle up as we delve into the fascinating world of Visual Regression Testing, exploring its definition, significance, processes, tools, benefits and challenges; shedding light on how it could be your secret weapon in maintaining a flawless user interface.

Brief explanation what is visual regression testing

Visual regression testing is a cool way of catching visual bugs in your application’s user interface. Think of it as a spellchecker for your UI – it compares the current state of a page with a baseline image to spot any visual discrepancies. It’s not just about finding layout issues, though. It can also help ensure that all the visual elements of your website are working as expected – from fonts and colors to images and animations.

So how does visual regression testing work? Well, it involves using automated visual testing tools to capture screenshots of web pages at different stages of the development process. These screenshots are then compared with baseline images (which are the standard or reference images) to find any differences. If there’s even a minor pixel difference, the test fails, and you get an alert. There are loads of tools out there for visual regression testing – some popular ones include Percy, Applitools, and PhantomCSS.

Now, manual visual testing has its place but let’s be real: it can be painfully slow and error-prone. And here’s where automated visual regression testing comes in handy:

  • It saves time by automating repetitive tasks.
  • It increases test coverage by checking every single visual element on your web pages.
  • It helps maintain brand image by catching inconsistencies before they reach users.
  • It reduces false positives (no more “oh, it was just a temporary glitch” moments).

Remember, though: while visual regression testing is super helpful at catching those pesky visual bugs, it doesn’t replace functional testing. You still need to make sure your buttons actually do what they’re supposed to do when clicked! But combining functional tests with dedicated visual regression tests can seriously level up your testing game and improve user experience.

Why is visual regression testing so important?

If you’re in the business of developing and managing applications, you know how crucial user experience is. And that’s exactly why visual regression testing is so important. It’s all about ensuring that your application looks the way it should on every platform and every version.

I mean, come on, how frustrating is it when you’re using an app, and there are visual bugs or discrepancies that just make the whole thing look amateurish?

Visual regression testing helps keep those pesky visual defects at bay by comparing the current state of your application with a baseline image (that’s basically a screenshot of what the application should ideally look like).

Now let’s get into the nitty-gritty of it. With visual regression testing tools, you can automate this process instead of doing manual visual testing which can be time-consuming and error-prone. Here are some things these tools offer:

  • They capture screenshots of web pages or mobile apps.
  • They compare these screenshots with baseline images.
  • They detect differences (even subtle ones that might slip past a human eye) between them.

Automating this process saves you time and improves test coverage. Plus, it decreases the chances of false positives. It’s like having a highly efficient test engineer who never sleeps or takes coffee breaks!

And here’s another reason why visual regression testing is a big deal: dynamic content. In today’s world where applications are constantly updated with new content, ensuring visual consistency can be quite a challenge. But with automated visual regression testing, you can insert visual checkpoints at various stages to make sure all the visual elements stay consistent no matter how many updates or changes are made.

Why traditional way of testing is limited?

The first thing that comes to mind is how insanely time-consuming it is. Think about it. Manual visual testing means your eyes are glued to the screen as you meticulously check every single pixel on a web page. Every button, every image, every text box – everything needs to be scrutinized for visual bugs. That’s not just exhausting; it’s also incredibly inefficient.

Then there’s the issue of accuracy. Let’s face it, we’re only human, and humans make mistakes. We might miss a visual defect or two after hours of repetitive testing. Even the most eagle-eyed test engineer can overlook subtle visual discrepancies that an automated visual testing tool could pick up in a heartbeat. This could lead to poor user experience, affecting your brand image.

Here’s what you should remember:

  • Manual visual regression testing is time-consuming.
  • The risk of overlooking visual bugs is high due to human error.
  • It might lead to a bad user experience and affect your brand image.

And let’s not forget about scalability. As your application grows, so does the number of pages you need to test. You can’t possibly scale up your manual testing efforts at the same pace without expanding your team significantly (and that means more salaries to pay!). Automated visual regression testing tools can handle these increasing volumes effortlessly and ensure comprehensive test coverage across all the visual elements in your application’s user interface.

Lastly, traditional visual regression testing struggles with dynamic content and different browser/operating system combinations. Trying to manually validate these scenarios is like trying to hit a moving target while blindfolded – good luck with that! Automated testing tools can handle these complex scenarios with ease, reducing false positives and ensuring accurate results.

Comparison of popular types of visual regression testing

Below you have quick comparison of most popular types of visual regression testing.

Manual visual testing

Manual visual testing is the old-school way of doing things – it’s like proofreading a document for typos. The tester manually checks all the visual elements on a webpage or app, looking for any visual bugs that might mess up the user experience. It can be time-consuming and tedious, but sometimes, it’s necessary to ensure that everything looks just right.

Automated visual regression testing

Automated visual regression testing takes manual testing to the next level. Instead of relying on human eyes to spot visual defects, we use automated testing tools. There are several types of automated tests you can run, but some of the most popular are DOM-based comparisons and pixel-by-pixel comparisons. DOM-based comparison checks the document object model (the HTML structure of your page) against a baseline image or code snapshot. If there are any differences (like missing elements or changed attributes), the test flags it as a potential bug. It’s a neat method, but it can throw up false positives – like if dynamic content changes between test runs.

Pixel-by-pixel comparison

Pixel-by-pixel comparison, on the other hand, compares screenshots of your web pages or apps at the pixel level against baseline images. It’s super precise and great for catching even tiny visual discrepancies but can also generate false positives if not used correctly (for instance if there’s an insignificant change in color shade).

Visual AI comparison

More recently, Visual AI comparison has come into play. This uses computer vision and machine learning algorithms to mimic how humans would visually compare screens, making it more intelligent than traditional automated tools. It’s capable of ignoring insignificant differences while focusing on those that impact user experience.


Okay folks, I hope that this article has provided you with a comprehensive understanding of what Visual Regression Testing is all about. I hope now you know what is going on with this whole complicated visual regression testing and feel more confident in implementing it in your future software development tasks. Remember, maintaining consistency in your application’s appearance is just as important as ensuring its functionality, making visual regression testing an invaluable practice in your development process.


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