Visual Regression Testing

Anushree Chatterjee

Imagine a popular e-commerce website that recently underwent a design update. While the core functionality remains intact, a minor CSS issue causes the product images to display incorrectly on certain browsers. Manual testing might overlook this subtle change. Even the slightest visual glitch, like a misplaced button or a color mismatch, can negatively impact user experience and brand reputation.

That is why automated visual regression testing is important. By automating the process of comparing visual snapshots of an application, you can quickly identify and address visual inconsistencies and ensure a seamless user experience.

Let’s review what visual regression testing is, the compelling benefits of automating visual regression tests, and how they can significantly enhance your software testing process.

What is Visual Regression Testing?

Visual regression testing is like proofreading a website or app for its looks. Imagine you’ve created a beautiful design, and every time you make changes to it, like adding a new feature or fixing a bug, you want to ensure nothing has accidentally gone out of place.

Why Automate Visual Regression Testing?

Automating visual regression testing is similar to doing it as a human, just like a machine does it for you. It’s like having a super-efficient helper who never misses a mistake, works around the clock, and saves you from hours of tedious work. It ensures that your website or app always looks and works as expected, even when you update or introduce new features. Automated visual regression testing mainly overcomes the challenges posed by doing the process manually.

Challenges of Manual Visual Regression Testing

• Time-Consuming: Manually comparing screens or pages pixel by pixel is extremely slow. Imagine comparing dozens (or even hundreds) of pages or designs. It’s exhausting and can take days.
• Human Error: People get tired, distracted, or miss small changes, especially subtle ones like a slightly moved button or a font size change. It’s easy to overlook something, especially when they have to keep doing the same thing over and over again.
• Inconsistent Results: Different people might notice different things. What one tester thinks is a problem, another might not. This inconsistency can lead to confusion or missed issues.
• Limited Coverage: Manually testing all browsers, devices, and screen sizes is nearly impossible. Most teams end up testing only a few, leaving gaps that could result in bugs for users.

How Does Visual Regression Testing Work?

If we were to look at how it works, here’s a simple summation of the visual regression testing process:

• Take a Picture of Your Design: Before making changes, you take a screenshot of how the website or app looks (this is your baseline).
• Make Changes: Now, you update the code, maybe fixing a button or adding new content.
• Spot the Difference: After the changes, you take another screenshot and compare it with the original. This is like playing a “spot the difference” game to catch anything that doesn’t look right, like buttons moving, text disappearing, or colors changing unexpectedly.

A Real-Life Example

Think of a busy online store. Every time they add a new product, update their design, or fix bugs, they risk breaking something visually, like a misaligned “Add to Cart” button. Manually testing every page would take forever and might still miss some issues. But with automation, the store can test every change instantly across all devices, ensuring everything looks perfect for customers.

Benefits of Automation Visual Regression Testing

Here are the benefits that you can enjoy from automated visual regression testing.

Saves Time

• Manual Testing Takes Forever!
  Imagine checking every page of a website to ensure nothing looks off. It’s a slow, tedious process.
• Automation Does It Faster.
  Automated tools compare images instantly, even for dozens or hundreds of pages. A task that could take hours manually can be done in minutes.
• Here’s an example.
  If you’re testing 50 pages across three screen sizes (desktop, tablet, mobile), manual testing might take all day. Automation can do it in a fraction of the time.

Increases Accuracy

• Humans Can Miss Details.
  After hours of testing, it’s easy to overlook small issues like a slightly shifted button or a color change.
• Automation Catches Everything.
  Tools compare the images pixel by pixel or use AI to highlight meaningful differences to ensure nothing is missed.
• Here’s an example.
  Automation will flag even a single-pixel shift in a logo or a barely noticeable font change, things that are often overlooked in manual checks.

Reduces Subjectivity of Human Interpretation

• Manual Testing is Subjective.
  Different testers might interpret visual changes differently. Some might miss an issue entirely or mark a minor difference as a problem.
• Automation is Objective.
  It applies the same rules every time, providing consistent results and reducing the chance of mistakes.
• Here’s an example.
  If a developer changes a color slightly, the tool will catch it consistently, no matter who is running the test.

Covers More Scenarios

• Manual Testing is Limited.
  Testing across multiple devices, browsers, and screen sizes manually is nearly impossible. It’s time-consuming and requires access to many environments.
• Automation Expands Coverage.
  Automated tools can test your app on different devices (phones, tablets, desktops) and browsers (Chrome, Safari, Edge) simultaneously.
• Here’s an example.
  With automation, you can ensure your app looks great on an iPhone, a Samsung tablet, and a Windows PC – all at the same time.

Improves Workflow Efficiency

• Fits into Your Development Process.
  Automation integrates with CI/CD pipelines, which means that tests run automatically whenever new code is pushed.
• Quicker Feedback.
  Developers can immediately see if a visual issue was introduced and fix it before it becomes a bigger problem.
• Here’s an example.
  Every time a developer submits changes, automated tests can run and notify them of any visual issues before the update is released.

Reduces Costs Over Time

• Manual Testing Costs Add Up.
  Paying testers to manually check visuals for every release gets expensive, especially for large projects with frequent updates.
• Automation is a One-Time Investment.
  While setting up automated tests requires some initial effort and cost, they save money in the long run by reducing manual work.
• Here’s an example.
  A team that updates its app weekly could save hundreds of hours (and thousands of dollars) annually by automating visual checks.

Improves Quality and User Experience

• Catch Visual Bugs Early.
  Automated tests catch layout issues, missing elements, or color inconsistencies before they reach users.
• Builds Confidence.
  Knowing your app has been thoroughly tested ensures it looks professional and works perfectly.
• Here’s an example.
  Automation can catch a misaligned “Buy Now” button or overlapping text before customers see it. This prevents frustration and preserves your brand image.

Reduces Stress for Your Team

• Manual Testing is Repetitive and Boring.
  Nobody enjoys staring at the same screens over and over.
• Automation Does the Boring Work for You.
  By letting tools handle repetitive tasks, your team can focus on more exciting and creative challenges.
• Here’s an example.
  Testers can spend more time analyzing deeper/masked bugs or brainstorming improvements instead of doing monotonous screenshot comparisons.

Handles Dynamic Content

• Dynamic Content is Hard to Test Manually.
  Pages with ads, live data, or animations change constantly, which makes manual comparisons tricky.
• Automation with AI Solves This.
  AI-powered tools can ignore irrelevant changes (like an ad refreshing) and focus only on meaningful differences.
• Here’s an example.
  A page with rotating banners or livestock prices can be tested without being flagged for every minor update.

Scales Easily as Your Project Grows

• Manual Testing Doesn’t Scale Well.
  As your app grows, manual testing becomes unmanageable.
• Automation Grows With You.
  Whether you have 10 or 1,000 pages, automation can handle it effortlessly.
• Here’s an example.
  An e-commerce site adding new products daily can automate tests to ensure consistent visuals across the entire site without additional manual effort.

Techniques for Visual Regression Testing

Here are the ways in which automation tools tend to handle visual regression testing.

Pixel-by-Pixel Comparison: The tool takes screenshots of your web pages before and after changes. It compares these images pixel by pixel to identify differences.

• Benefits
  • Very precise: It can detect even the smallest visual changes, like a one-pixel shift or a tiny color change.
  • Easy to set up and understand.

DOM-Based Comparison: Instead of comparing images, this method checks the structure of the webpage (its Document Object Model or DOM). It looks for changes in elements like text, buttons, or images by analyzing their properties (size, color, position).

• Benefits
  • Less affected by small visual rendering differences (e.g., fonts or pixel smoothing).
  • Faster than pixel-by-pixel comparisons because it doesn’t rely on image processing.

Screenshot Comparison with AI Assistance: Combines pixel-by-pixel comparison with AI to analyze changes. AI helps filter out unimportant differences (like minor rendering variations) and focuses on significant ones (like missing buttons or layout shifts).

• Benefits
  • Reduces false positives: AI can ignore dynamic or unimportant changes, like ads or timestamps.
  • Smarter and more adaptable than traditional pixel-by-pixel methods.

Layout Comparison: Instead of comparing every pixel, this method checks the layout of the page. It looks at the structure of elements (like positions, sizes, and spacing) to see if anything has shifted or broken.

• Benefits
  • Good for catching layout problems, such as overlapping text or elements moving out of place.
  • Faster than pixel-by-pixel comparison.

Choosing the Right Method

The best method depends on your needs:

• Project complexity: For simple applications, manual or layout comparison might suffice. For complex UIs, AI-powered or pixel-by-pixel comparison is more suitable.
• Sensitivity to visual changes: If you need to detect even subtle changes, pixel-by-pixel comparison is ideal. For major layout shifts, layout comparison or DOM-based comparison might be sufficient.
• Team expertise: If your team has limited technical expertise, manual or no-code tools might be a good starting point. For more advanced teams, AI-powered tools can provide more sophisticated analysis.

Visual Regression Testing Tools

Selecting a tool for visual testing can be a challenge. Quite often, visual regression testing is just a part of the entire STLC process. Hence, it doesn’t make sense to exhaust one’s budget on a separate tool altogether. Moreover, you’d want to pick a tool that is easy to use, provides reliable test results, can integrate with CI/CD pipelines for continuous testing, and offers easy test maintenance. A great alternative that satisfies all these conditions is testRigor.

testRigor is a generative AI-powered test automation tool. If you’re looking for a solution that lets you take care of visual regression testing along with functional regression testing, then this tool should be your go-to. You can easily create tests in plain English language across different platforms and browsers.

testRigor lets you compare screenshots and even determine how much variation in them is acceptable for a test case to be deemed as passed. testRigor is an intelligent tool and it uses Vision AI to perform visual UI testing, exploratory testing, OCR, self-healing, visual recognition, screen navigation, and so forth.

Here’s a detailed guide on How testRigor Allows Automated Visual Testing.

Best Practices for Automated Visual Regression Testing

Here are some best practices to make your automated visual regression testing efficient, accurate, and reliable, explained in simple terms:

Start with a Strong Baseline

Take clear and accurate screenshots of your app or website in its current, correct state. These will serve as the “before” images for future comparisons.

Why It’s Important: Without a reliable baseline, you won’t know what’s actually changed or if the change is intentional.

Tip: Update the baseline only after thoroughly verifying changes are correct and intended.

Focus on Critical Areas For Visual Regression

Prioritize testing areas that matter most to users, like navigation menus, buttons, forms, and checkout flows.

Why It’s Important: Testing everything can be time-consuming and unnecessary. Focus on high-impact parts of your app.

Example: For an e-commerce site, prioritize the product page and payment section over less-used pages.

Define Thresholds for Changes

Set tolerances for acceptable differences, such as ignoring small shifts in pixels or color variations that don’t affect usability.

Why It’s Important: This helps avoid false positives, which saves time by reducing noise in your test results.

Tip: Use tools that allow you to customize thresholds or use AI to differentiate meaningful changes.

Handle Dynamic Content

Ignore or mask areas with dynamic elements like ads, timestamps, or live data that change frequently.

Why It’s Important: Dynamic content can create false positives and make it harder to find real issues.

Tip: Configure your testing tool to exclude these areas or use AI-assisted tools that can intelligently ignore them.

Run Tests Across Multiple Browsers and Devices

Test how your app or site looks on different browsers (Chrome, Safari, Edge) and devices (desktop, tablet, mobile).

Why It’s Important: Users access apps on various platforms, and visual bugs might only appear in specific environments.

Tip: Use tools that support cross-browser and responsive testing.

Integrate With Your CI/CD Pipeline

Set up your visual regression tests to run automatically whenever developers push new code or updates.

Why It’s Important: This ensures bugs are caught early and keeps your development workflow smooth.

Review and Update Baselines Regularly

Update your baseline images when legitimate design changes occur, but only after validating the changes.

Why It’s Important: Keeping outdated baselines can lead to irrelevant failures, slowing down your workflow.

Tip: Use version control to track baseline updates for easy rollback if needed.

Keep Tests Maintainable

Write clear, reusable test scripts and organize your test cases logically. Read: How to Write Maintainable Test Scripts.

Why It’s Important: As your app grows, poorly structured tests can become unmanageable.

Tip: Group tests by features or components for easier maintenance.

Monitor Test Results Closely

Regularly check test results to review flagged differences and address any issues promptly. Read: Understanding Test Monitoring and Test Control.

Why It’s Important: Ignoring test results can lead to bugs slipping through or unnecessary work to clean up later.

Tip: Use tools with detailed visual reports and notifications (e.g., email, Slack) to keep your team informed.

Use AI-Powered Tools for Smarter Testing

Use tools that use AI to distinguish between meaningful visual changes and irrelevant ones.

Why It’s Important: This reduces false positives and helps you focus on real issues.

Tip: Tools like testRigor are good for the job since it allows test scripts to adapt to changes in UI and saves maintenance efforts.

Regularly Evaluate Your Tool

Periodically review whether the tool you’re using meets your needs as your project grows.

Why It’s Important: The best tool for your current setup might not work as well for a larger or more complex app.

Tip: Stay informed about new tools and features to ensure you’re using the best option available.

The Bottom Line

Automating visual regression testing isn’t just about making things easier. It’s about building confidence. You can roll out updates faster, knowing your app or website still looks perfect. Like what automation does, automating this process saves time, reduces errors, and ensures your app or website always looks professional and polished. It turns a tedious, error-prone task into a quick, reliable process that gives your team peace of mind and your users a flawless experience.

Pick a suitable tool for the automation process, and your visual regression testing efforts will pay off.

“We spent so much time on maintenance when using Selenium, and we spend nearly zero time with maintenance using testRigor.”

Keith Powe VP Of Engineering - IDT