Automated Visual Testing with Selenium & Applitools

In the fast-paced world of web and mobile application development, delivering a seamless user experience is just as important as ensuring functional correctness. While traditional functional testing focuses on verifying if buttons work, forms submit correctly, and pages load as expected, it often overlooks a crucial aspect — how things look on the screen. This is where visual testing steps in.

Visual testing goes beyond checking functionality; it ensures that the application’s user interface (UI) appears as intended. It helps detect visual bugs like misaligned elements, overlapping text, incorrect fonts, broken layouts, or color inconsistencies — issues that functional tests usually miss.

Imagine a scenario where a “Submit” button works perfectly, but due to a CSS update, it’s now hidden behind an image. Functional tests would pass since the button technically works, but a real user would still face a broken experience. Visual testing catches these UI glitches by comparing screenshots of the application against a baseline (expected design) and highlighting even the smallest visual differences.

With modern applications being responsive — adapting to different devices and screen sizes — visual validation becomes even more essential. It ensures a consistent and polished look across desktops, tablets, and mobile devices. As users expect pixel-perfect interfaces, integrating visual testing into your test automation strategy helps prevent visual regressions and strengthens the overall quality of your software.

What is Visual Testing?

Visual testing is a type of software testing that ensures the UI (User Interface) of an application appears correctly to users across different browsers, devices, and screen sizes. Unlike functional testing, which verifies the logic and behavior of an application, visual testing focuses on identifying visual defects such as misaligned elements, font inconsistencies, broken layouts, or color mismatches.

For example, if a button shifts slightly due to a CSS change, functional tests may still pass, but visual tests will detect the discrepancy.

Why Traditional Functional Testing Misses Visual Bugs?

Functional testing tools like Selenium, Cypress, and Playwright are excellent at verifying functionality—ensuring that buttons work, forms submit correctly, and calculations return expected results. However, they do not check how elements are displayed on the screen.

Here are a few limitations of functional testing in detecting UI issues:

• Pixel-level UI issues go unnoticed (e.g., overlapping text, incorrect font sizes).
• Cross-browser inconsistencies are not caught (e.g., a layout breaking in Safari but working fine in Chrome).
• Dynamic content variations (ads, pop-ups) can disrupt layouts, but functional tests won’t detect these subtle shifts.
• Responsiveness issues (e.g., a menu displaying incorrectly on a smaller screen) are ignored unless explicitly coded into tests.
• Since functional testing tools focus on verifying DOM elements and interactions, they miss visual defects that can degrade the user experience.

How Visual Testing Improves UI Consistency and User Experience?

Visual testing tools like Applitools help maintain a consistent look and feel across all UI components. By incorporating AI-powered visual validation, teams can:

• Ensure UI Consistency: Detects unintended UI changes across different screens, browsers, and devices.
• Identify Layout Breaks Early: Find issues like hidden elements, overlapping sections, or broken grids before they reach production.
• Improve Development Workflow: Provide fast feedback to designers, developers, and testers, reducing iteration cycles.
• Enhance Brand Perception: A polished, visually accurate UI increases customer trust and engagement.

Introduction to Applitools: AI-Powered Visual Validation

Applitools Eyes is an AI-driven visual testing platform that extends Selenium’s capabilities by performing intelligent image-based comparisons. Unlike traditional pixel-by-pixel comparison tools, Applitools uses computer vision and AI to identify true UI defects while ignoring insignificant differences, such as anti-aliasing or minor rendering variations.

Key Features of Applitools:

• AI-Powered Visual Comparisons: Detects even the smallest UI differences while ignoring irrelevant rendering variations.
• Baseline Image Matching: Stores reference snapshots (baselines) and compares new test runs to detect unexpected UI changes.
• Cross-Browser and Cross-Device Testing: Ensures a consistent UI appearance across Chrome, Firefox, Edge, Safari, mobile browsers, and native apps.
• Smart Region Matching: Allows testers to ignore dynamic content (such as timestamps, ads, or rotating banners) to avoid unnecessary test failures.
• Auto-Maintenance and Smart Test Management: Uses AI to categorize changes (intentional vs. unintentional), reducing manual test maintenance.
• CI/CD and Cloud Integration: Seamlessly integrates with Jenkins, GitHub Actions, Azure DevOps, and other CI/CD tools for automated visual testing in pipelines.

How Applitools Complements Selenium with Visual Assertions

By integrating Applitools with Selenium, testers can extend Selenium’s functional tests to include visual verification, ensuring that both behavior and UI appearance are validated.

How the Integration Works:

1. *Selenium Automates User Actions *– Selenium performs functional steps such as opening a webpage, clicking buttons, and submitting forms.
2. Applitools Captures Visual Snapshots – After each significant step, Applitools captures a screenshot of the entire page or specific elements.
3. Applitools Compares the Screenshots with Baselines – The new image is automatically compared to the baseline snapshot stored from previous test runs.
4. AI-Powered Analysis Flags Visual Differences – If any unexpected UI changes are detected, Applitools marks them for review in the Test Manager dashboard.

What is Applitools Eyes?

Applitools Eyes is an advanced AI-powered platform for testing various user interfaces, including websites, web applications, native mobile apps, documents, and media. Unlike traditional automation tools that validate test scenarios mechanically, Applitools leverages artificial intelligence to analyze thousands of UI elements and scenarios instantly, mimicking human-like visual perception for more accurate testing.

Understanding Applitools Baselines in Detail

What is a Baseline in Applitools?

A baseline in Applitools is a reference snapshot of your application’s UI. It serves as the expected appearance of the application, and all future test runs are compared against it to detect visual differences.

Unlike traditional assertion-based testing, which checks only functional correctness, Applitools performs pixel-by-pixel comparisons to catch visual defects, including layout shifts, color mismatches, missing elements, and responsive design issues.

Why Are Baselines Important?

1. UI Consistency: Verifies that your app maintains a uniform look across different versions.
2. Visual Bug Detection: Captures unintended UI changes, such as misalignments or missing elements.
3. Cross-Browser Compatibility: Identifies differences in UI rendering across different browsers and devices.
4. Regression Testing: Ensures that new changes don’t break the existing UI.

Lifecycle of a Baseline in Applitools

The baseline lifecycle consists of three main stages:

• First Test Run – Creating the Baseline

When you run an Applitools test for the first time, it:

• Captures a screenshot of the UI.
• Saves this image as the baseline in the Applitools dashboard.
• Stores metadata such as viewport size, browser, OS, and test name to ensure accurate comparisons in future runs.

Example: Suppose you are testing an e-commerce website where the “Add to Cart” button is green. During the first test run, Applitools captures and stores this design as the baseline.

• Subsequent Runs – Comparing Screenshots with Baseline

In later test runs, Applitools:

• Captures a new screenshot of the webpage.
• Compare it pixel-by-pixel with the saved baseline.
• Highlights any differences (color changes, missing elements, layout shifts, etc.).

Example: If a CSS update turns the “Add to Cart” button red, Applitools detects the difference and flags it for review.

Handling Differences – Approving or Rejecting Changes

When Applitools detects visual changes, the tester has three options:

Accept the Change (Update Baseline)

• If the change is expected, approve the new screenshot as the baseline.
• Future test runs will now compare against this updated version.

Reject the Change (Bug Found)

• If the change is unexpected, report it as a UI bug.
• Developers can fix the issue before pushing changes to production.

Ignore Specific Differences (Dynamic Elements)

• If elements like ads, timestamps, or user-generated content change frequently, you can mark them as dynamic regions to avoid false positives.

Example: If the “Add to Cart” button turns red instead of green due to a design update, the tester can approve this as the new baseline. But if the button disappears entirely, the tester would reject the change as a bug.

Key Attributes That Define a Baseline

Each baseline is uniquely identified using multiple attributes:

Test Name

• Each visual test has a unique name assigned in Applitools.
• Example: “Homepage Visual Test”

Application Name

• Applitools associates baselines with a specific application to avoid mix-ups between projects.
• Example: “E-Commerce App”

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