Guide to Visual Testing: Ensure a Pixel-Perfect User Experience

What Is Visual Testing?

Visual testing is a form of software testing that assesses the visual fidelity of your user interface (UI) or graphical user interface (GUI). It evaluates the actual visible output of your application against the expected results and thus helps you catch and fix “visual bugs” in a page or screen.

Typically, these visual bugs tend to be missed by other types of UI tests, like functional tests. To deliver a flawless webpage experience, you’ll want to invest in functional and visual testing.

You can conduct visual testing on individual components as well as on the application as a whole. Several automated visual testing tools are available on the market that can enhance the speed and accuracy of the process—we’ll discuss them later in detail.

Who Uses Visual Testing?

There are several people involved in ensuring that your visual testing happens smoothly and in sync with other kinds of testing:

• Web designers: They verify that the app is suitably in line with their design concepts and adheres to the brand guidelines.

• Front-end testers: They check that the app is visually consistent and responsive across all browsers, devices, and screens.

• QA experts: They ensure that the entire app has design fidelity by meticulously inspecting and validating its visual aspects.

• Manual testers: They check the UI for visual quality and highlight any design discrepancies that might have been missed.

Features of Visual Testing

Here are the main components of any visual testing process:

• Testing UI elements: Visual testing verifies that UI elements like text fields, images, buttons, and other graphical components are positioned exactly as they should be according to the design.

• Testing theme and color: The app’s branding should comply with design guidelines, with uniform appearance and saturation across devices.

• Testing text and fonts: Visual testers check that all content appears in the correct font style and size and that all text is readable and formatted correctly.

• Design coherence: Visual testing ensures the app’s design and arrangement stay consistent across different screen sizes and resolutions.

Advantages of Visual Testing

Along with functional testing and performance testing, visual testing has emerged as one of the most valuable tools for ensuring that your app looks and behaves exactly as it should. There are multiple advantages to investing in visual testing, including:

1. Efficient cross-browser and cross-device testing

Visual testing tools can automatically run tests on UI behavior across devices and browsers to ensure that end users in all environments get a uniform and high-quality experience. The tools are particularly useful for catching issues that only occur under specific conditions, such as a glitch in image loading on an older model of iPhone.

2. Improved regression testing

Visual testing tools can quickly compare screenshots of your current UI with a defined baseline to ensure that any UI changes you introduce don’t cause unintentional visual regressions. Moreover, automated tools can adapt much faster to UI changes than traditional testing scripts, making them more suitable for dynamic environments.

3. Enhanced user experience

Your end users will access the app from various platforms and expect a consistent experience regardless of where they log in.

With visual testing, you can ensure that the UI is consistent across devices, operating systems, browsers, and screen resolutions.

Moreover, visual testing focuses on the end user’s point of view, which means your testers access the UI just like a user would and can accurately highlight any differences or glitches in the navigation experience. This makes for a more polished app than one that has relied on backend testing alone.

4. Detection of visual bugs

Visual testing helps you quickly spot visual issues like overflowing text, improperly rendered color palettes, or images that are misaligned on iOS but look fine on Android. These aren’t functional issues per se, but they can negatively affect the aesthetics of your app and create a poor impression in the end user’s mind unless corrected.

5. Automation efficiency

With automated visual testing, chances of human error immediately go down. You can now rapidly test thousands of pixels within a few seconds and be assured of the accuracy of the results.

Moreover, when you integrate visual testing into your CI/CD pipeline, your developers can instantly get feedback on how the app’s visuals have changed with each code change, helping them detect and fix any visual issues much sooner.

Disadvantages of Visual Testing

While visual testing has many benefits, it’s not without drawbacks. When you select a visual testing tool, you’ll consider these factors.

1. False positives

Visual tests might sometimes flag false positives, such as minor rendering differences that don’t affect the user experience. Investigating those can take up unnecessary time and resources from your time.

Another area with the potential for false positives is dynamic content, such as date or time stamps, which by default display different results each time. Your testing team will need to bake in extra configuration for those elements.

2. Resource intensive

Running visual tests across different end-user environments can be highly resource-intensive, which could potentially slow down your continuous integration and deployment (CI/CD) process. Moreover, storing your baseline images and results can take up a lot of space, particularly with complex UIs, which can further increase your overhead.

3. Difficult to set up and maintain

Setting up a visual testing framework can be costly and complicated as you configure your testing environments and integrate the testing tool with your CI/CD pipelines. Plus, as your UI evolves, you’ll need to keep upgrading the baseline designs, which can quickly become cumbersome.

4. Tool limitations and dependencies

How effective your visual testing is depends almost entirely on which tool you’re using. Not all tools are equally good at testing across diverse environments or handling dynamic content. When introducing a visual testing tool, your team will also be involved in the learning curve. The longer your testers take to become familiar with it, the more your processes will slow down.

5. Limited detection of functional issues

Visual testing focuses on your app’s appearance and won’t detect issues like faulty data handling or workflow errors that don’t directly impact the UI. Therefore, you’ll need to run visual testing alongside your functional testing methods.

Steps for Implementing Visual Testing

Implementing a sound visual testing process involves multiple steps, some of which might look different depending on your development workflow. In general, though, these are the steps you want to keep in mind:

1. Define objectives and scope

Start by determining exactly what you want to accomplish with visual testing. Are you looking to ensure cross-browser consistency, detect layout issues, or verify that the site branding adheres to the guidelines?

Then, select and prioritize the parts of your app that need visual testing, such as critical user flows or UI components that often change, such as popups with the latest promotions.

2. Choose the right testing tool

Do your research on the different types of testing tools available, and conduct trial runs to see which one best fits your project environment. Evaluate them on criteria like cross-browser and cross-device support, ease of use, CI/CD integration, ability to handle dynamic content, and so on.

3. Set up your testing environment

Make sure your testing environment is ready to implement visual testing. Have baseline images of your UI ready as a reference for visual tests, and keep them stored in version control along with your code. This helps with tracking UI changes over time.

4. Integrate with the CI/CD pipeline

By integrating your visual tests with your CI/CD pipeline, you ensure that the tests are run automatically with each code commit or pull request and can provide instant feedback on visual regressions. In addition, consider investing in a tool that supports parallel testing across multiple browsers and devices, saving you time.

5. Configure and fine-tune your tests

To avoid false positives, you’ll need to take some time to configure your testing tool for optimal results. For instance, you can write custom scripts to stabilize dynamic elements like timestamps before taking screenshots.

You can also set acceptable thresholds for visual differences, such as a small pixel difference between a desktop and a mobile device.

6. Run initial tests and review the results

Perform your first round of visual tests, then use that to establish a baseline and identify any issues that immediately pop up. Review everything carefully, and once you’re satisfied, add the baseline images to storage for future comparisons.

7. Establish a clear review process

Collaborate with your developers, designers, and QA engineers to set up a clear process for reviewing and addressing test failures and determining which issues require intervention. This way, everyone is clear on the standards to be met and can resolve problems efficiently and without too much back-and-forth.

8. Invest in continuous maintenance and updates

As your app evolves, you’ll need to update your baseline images to reflect any intentional UI changes for maximum test accuracy. You’ll also need to review and refine your test configurations and thresholds as necessary.

9. Document and educate

Be sure to document every step of the visual testing process so that all future testers follow a consistent workflow.

You should also invest in training your team on visual testing best practices and how to interpret the test results. This ensures that everyone on your team is invested in upholding visual quality and consistency on the app.

10. Scale and optimize

It’s important to expand the scope of your visual testing as your app grows so that you always prioritize the components that have the most impact on user experience. You should also keep optimizing the testing process by reducing test execution time or enhancing your parallel testing capabilities.

Visual Automation Testing Methods

Let’s take a look at the common techniques you should know about.

1. Pixel-by-pixel comparison

This is a method where the current screenshot of a UI is compared against a baseline image on a pixel level. It’s highly precise, catching even the smallest differences in the UI’s visual appearance.

However, Pixel-by-pixel comparison is also very sensitive, which means it might flag minor, irrelevant changes, like rendering differences between browsers, as potential issues.

It works best for applications where maintaining pixel-perfect accuracy is critical, such as in high-fidelity design environments.

2. DOM-based comparison

If you want to focus on the structure and layout of the web page by comparing the Document Object Model (DOM), then DOM-based comparison is apt. Instead of looking at the rendered pixels, it checks for changes in the layout and structure of HTML elements.

This method helps ensure that the overall layout remains consistent, even if minor differences in appearance don’t affect the user experience. It’s particularly effective for testing applications where the layout’s integrity is more important than exact visual matching.

3. Layout comparison

This technique checks whether UI elements are placed correctly relative to each other, ensuring that the overall structure of the page is intact. Layout comparison is handy for responsive designs, where the placement of elements can change based on screen size and orientation.

While it doesn’t scrutinize the content within the elements, it ensures that the design layout adapts correctly across different devices.

For example, a retail website might use layout comparison to ensure that product grids and navigation menus remain properly aligned when viewed on mobile devices, tablets, and desktops.

4. Screenshot comparison

It involves taking screenshots of the entire page or specific components and comparing them with baseline images. This method provides a comprehensive view of the UI’s visual state, capturing everything from colors and fonts to images and layouts.

Screenshot comparison is easy to implement and widely supported by visual testing tools. However, it can be resource-intensive and may require managing large amounts of image data.

A web app that frequently updates its user interface might use screenshot comparison during its CI/CD process to detect visual regressions before the new code is deployed automatically.

5. Visual regression testing

This automated process compares the current version of an application against previous versions to identify unintended visual changes.

Visual regression testing is highly effective when integrated into CI/CD pipelines. It provides immediate feedback on visual issues as the application evolves.

For example, a large eCommerce platform might apply this technique to ensure that updates to the checkout process don’t introduce visual errors, such as misplaced buttons or incorrect color schemes, across different site versions.

6. AI and Machine Learning (ML)-based testing

Advanced visual testing tools leverage AI and ML algorithms to analyze visual differences intelligently. These technologies help identify changes that significantly impact the user experience while ignoring trivial variations.

Over time, the AI learns from past results, improving its accuracy. This method is beneficial for reducing false positives and handling dynamic content more effectively, though it requires more sophisticated tools and can be more expensive to implement.

A social media platform might use AI-based visual testing to ensure that user-generated content is displayed correctly across various devices, filtering out minor rendering differences that don’t affect usability.

7. Perceptual comparison

It compares images based on how they appear to the human eye rather than on a strict pixel-by-pixel basis. Perceptual comparison focuses on visual differences that would be noticeable to users, making it more aligned with human perception.

It helps reduce noise from insignificant differences and focus on changes that truly impact the user experience.

8. Component-level testing

This method isolates individual UI components for testing in a controlled environment rather than testing the entire application simultaneously.

Component-level testing is instrumental in applications built with reusable components. It allows you to test each component’s visual integrity independently. It’s scalable and helps detect issues early in the development process.

9. Cross-device and cross-browser testing

As the name suggests, this involves running visual tests across different devices and browsers to ensure that the application’s appearance remains consistent. Cross-device and cross-browser testing are essential for applications that must work seamlessly across various environments.

For instance, a banking app might use techniques to ensure that its UI remains consistent and functional on all supported browsers and devices, including older browser versions and low-resolution screens.

Cross-browser and cross-device testing combine other visual testing techniques with browser automation tools to achieve broad coverage, though it can be resource-intensive to maintain.

10. Manual visual testing

Despite the rise of visual automated testing, doing it manually also remains a valuable method. Manual testing involves human testers manually inspecting the UI for visual defects. It leverages human intuition and the ability to apply context-based judgment, making it possible to catch subtle issues that automated tests might miss.

Manual testing is often used in conjunction with automated methods to provide a final quality check before release.

For example, before launching a major update, a gaming company might employ manual visual testers to review the game’s UI across different levels and screens, ensuring that the visual experience aligns with the design intentions.

Visual Testing Tools to Know About

1. TestGrid

Are you looking for a robust automated visual testing solution for detecting even the slightest deviations in the appearance of web pages and mobile apps? Look no further than TestGrid.

Our platform ensures pixel-perfect precision across various devices and browsers, making it essential for delivering flawless user experiences.

With advanced testing capabilities, it streamlines visual testing, allowing you to efficiently identify and correct any inconsistencies in your apps’ visual presentation.

One of the standout features of TestGrid’s visual testing is its seamless automation. You can integrate this testing without the need for external SDKs or significant changes to your existing functional test case code.

With just a few lines of code, TestGrid’s AI takes care of the rest, automatically generating visual testing comparisons with baseline and subsequent tests. This built-in feature eliminates the need for feature-specific tools.

Additionally, its Visual AI capabilities extend the scope of traditional visual testing by validating every element within an interface, including text, images, layouts, and videos.

This approach ensures that the user interface looks correct on any device or screen size, particularly in complex test scenarios like BFSI (Banking, Financial Services, and Insurance) and eCommerce flows.

2. Applitools

Applitools is a well-known visual testing platform that uses AI to perform sophisticated visual comparisons. It can detect meaningful visual differences using AI, reducing false positives. It supports cross-browser testing and dynamic content handling and can be integrated into various testing frameworks like Selenium, Cypress, and WebDriverIO.

While not open-source, Applitools Eyes offers a free tier for smaller projects and open-source initiatives.

3. Selenium

Selenium is one of the most popular open-source tools for automating web browsers. It can be adapted for visual testing through integrations with other libraries.

While it itself is primarily focused on functional testing, it can capture screenshots during test runs, which can then be compared to baseline images using other tools like ImageMagick or third-party libraries like SeleniumBase.

This capability makes Selenium a versatile option for teams that want to combine functional and visual testing in a single framework.

4. BackstopJS

BackstopJS is a widely used open-source tool specifically designed for visual regression testing. It captures screenshots of web pages and compares them against baseline images, highlighting any visual differences.

It’s highly configurable, making it suitable for projects of all sizes. Users can define scenarios, set custom viewports, and run tests in parallel to optimize performance.

5. Percy

Although not fully open-source, Percy provides a free tier and is often used in open-source projects. It automates visual testing by capturing UI screenshots and comparing them against previous versions, highlighting any visual changes that may have occurred.

The platform provides detailed visual diffs, allowing developers to identify and address visual regressions quickly.

Final Words

In a world where apps are a dime a dozen and user expectations are increasing daily, visual testing is a key asset for fine-tuning an app experience to be as delightful as possible.

Despite their drawbacks, automated visual testing tools can enhance your testing capabilities. They let you continuously fine-tune the user experience and scale up to reach an ever-wider audience.

As always, remember to keep checking in with your QA team so that they’re getting the most out of the visual testing tool. You’ll soon be on your path to success.

Source: This article was originally published at https://testgrid.io/blog/visual-testing/