A Comprehensive Guide to Visual Regression Testing with LambdaTest

In the fast-paced world of web development, ensuring a consistent and visually appealing experience is of utmost importance. Visual regression testing is an important function that helps developers and QA staff identify and fix visual errors and inconsistencies between different versions of a web application. In this article, we will explore the importance of visual regression testing, introduce LambdaTest as a powerful tool for conducting these tests, and highlight its significant features and capabilities.

LambdaTest is a unified intelligent digital experience testing platform that allows businesses to test their websites on more than 3000+ test environments and real device clouds. It helps enterprises to test websites on all possible real-world scenarios to give users a seamless experience and bug-free deployment.  

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1: Understanding Visual Regression Testing

Visual regression testing is a testing process that focuses on detecting and highlighting any visual changes or discrepancies between two versions of a web application. Its role is critical in maintaining a consistent and visually appealing user experience. While traditional functional testing primarily focuses on validating the functionality of the application, visual regression testing goes beyond that by analyzing the layout, styling, and visual elements of the application.

One of the primary differences between visual regression testing and traditional functional testing is the scope of testing. Functional testing aims to validate whether an application’s features work as intended, while visual regression testing focuses on the presentation layer. This includes checking for visual defects caused by CSS changes, responsive design issues, font rendering differences, and more.

Maintaining visual consistency in web applications is challenging due to several factors. Different browsers, operating systems, and devices can render web pages differently, leading to discrepancies in the visual appearance. Additionally, frequent updates and changes to a website’s codebase can introduce unintended visual defects. With the multitude of combinations to consider, manually inspecting for visual inconsistencies becomes impractical. Visual regression testing automates this process and helps teams catch visual bugs before they reach the end users.

Section 2: Getting Started with LambdaTest

LambdaTest is a cloud-based cross-browser testing platform that provides a comprehensive solution for visual regression testing. Its key features make it a powerful tool for developers and QA professionals.

LambdaTest offers a vast collection of real browsers and operating systems, allowing users to test their web applications across various configurations. By signing up and onboarding with LambdaTest, users gain access to a cloud-based testing environment that eliminates the need for setting up multiple physical devices or virtual machines.

Integrating LambdaTest with popular testing frameworks like Selenium and Cypress is seamless. The platform provides robust documentation and easy-to-use APIs, making the integration process smooth for both beginners and experienced users.

Section 3: Setting Up and Running Your First Visual Regression Test with SmartUI and LambdaTest

Visual regression testing is a powerful technique to ensure the consistent appearance and user experience of web applications across various browsers, devices, and configurations. LambdaTest’s SmartUI makes it even easier to perform visual regression tests by simplifying the setup and execution process. In this section, we will guide you through the steps to set up your first visual regression test using SmartUI and LambdaTest.

Prerequisites:

Before getting started, ensure that you have a basic understanding of Selenium and WebDriver. Additionally, you need a LambdaTest account to access SmartUI features.

Step 1: Login to LambdaTest SmartUI

1. Go to the LambdaTest website (https://www.lambdatest.com/) and log in with your credentials.
2. Access your hub for Selenium remote connection instances at hub.lambdatest.com/wd/hub.
3. Copy your LambdaTest username (LT_USERNAME) and access key (LT_ACCESS_KEY) from the Access Key button located on the top right of the LambdaTest dashboard.

On MacOS/Linux, you can set the environment variables using the following commands:

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export LT_USERNAME=”YOUR_USERNAME”

export LT_ACCESS_KEY=”YOUR_ACCESS_KEY”

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On Windows, you can set the environment variables using the following commands:

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set LT_USERNAME=”YOUR_USERNAME”

set LT_ACCESS_KEY=”YOUR_ACCESS_KEY”

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Step 2: Create a SmartUI Project

1. Go to the Projects page on LambdaTest.
2. Click on the “New Project” button.
3. Select “Web” as the platform for executing your Selenium tests.
4. Add a name for the project, approvers for the changes found, and tags for filtering or easy navigation.
5. Click on the “Submit” button to create the SmartUI project.

Step 3: Configure Your Test with Selenium Desired Capabilities

Now that you have created a SmartUI project, you can generate screenshots by running automation scripts. Follow the steps below to configure your test with Selenium Desired Capabilities:

1. Clone the sample GitHub repository for SmartUI with Node.js (https://github.com/LambdaTest/smartui-node-sample).
2. Set up the LambdaTest credentials by following the instructions mentioned in the README.md file of the repository.
3. Edit the required capabilities for your test suite. Replace the following placeholders with your desired values:

– `platform`: Configure your OS for the Selenium test.

– `browserName`: Configure your browser for the Selenium test.

– `version`: Configure your browser version for the Selenium test.

– `visual`: Set to true to enable capture screenshots for the Selenium test.

– `name`: Name of the test for Selenium.

– `build`: Name of the build for Selenium.

– `smartUI.project`: Replace `` with the name of your project created in Step 2.

– `smartUI.build`: Replace `` with the name of the build.

– `smartUI.baseline`: Set to false to disable updating to a new baseline build.

Here’s an example of the capabilities configuration:

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let capabilities = {

  platform: “Windows 10”, // Configure your OS for Selenium test

  browserName: “chrome”, // Configure your Browser for Selenium test

  version: “latest”, // Configure your Browser Version for Selenium test

  visual: true, // Configure your Capture screenshot  for Selenium test

  name: “test session”, // name of the test for Selenium

  build: “Automation Build”, // name of the build for Selenium

  “smartUI.project”: “”, // Replace the name of the project with the new project name

  “smartUI.build”: “”, // Replace the name of Build with the new Build name

  “smartUI.baseline”: false, // Enable if you want to update to a new baseline build

};

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4. Connect to the LambdaTest Selenium Cloud Grid with SmartUI using the provided credentials:

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let gridUrl =

  “https://” +

  “” +

  “:” +

  “” +

  `hub.lambdatest.com/wd/hub`;

// Here is your Remote WebDriver Connection

let driver = await new webdriver.Builder()

  .usingServer(gridUrl)

  .withCapabilities(capabilities)

  .build();

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Step 4: Capturing Screenshots

Now that your test is set up and connected to the LambdaTest Selenium Cloud Grid with SmartUI, you can start capturing screenshots for visual regression testing.

For capturing a full-page screenshot, add the following webhook to your test cases where you want to capture the screenshot of your application:

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driver.executeScript(“smartui.takeFullPageScreenshot=”);

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For capturing a regular screenshot of a specific segment of your application, add the following webhook below the segment of the Selenium script where you want to take the screenshot:

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driver.executeScript(`smartui.takeScreenshot,{“screenshotName”:””}`);

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Step 5: Executing the Test

Before executing the test, install the dependencies by running the following command in the terminal:

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npm i

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Now, execute the test using the following command:

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node test.js

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Step 6: Checking the Test Results

After executing the test, you can check the executed builds over at LambdaTest SmartUI. Here, you can explore multiple features and execute more builds.

To fetch the status of the captured screenshot and the results, you can use the following webhook:

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driver.executeScript(“smartui.fetchScreenshotStatus”);

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The webhook will return the status of the screenshot captured, including the screenshot name, URL, status, mismatch percentage, threshold, browser used, resolution, build ID, build name, and project name.

Section 4: Running Visual Regression Tests at Scale

Running visual regression tests at scale offers several benefits for web development teams. Firstly, it enhances test coverage, allowing teams to test their applications across numerous browser and device combinations. This comprehensive testing helps identify browser-specific visual defects, ensuring a smooth user experience for all users.

LambdaTest’s parallel testing capability enables running multiple tests concurrently, significantly reducing test execution time. This is especially important in today’s fast-paced development environment, where quick feedback is crucial for maintaining agility.

To optimize test environments, LambdaTest allows users to run tests on a wide range of browser versions, operating systems, and devices. This ensures that the application is tested on the platforms that matter most to end-users. Additionally, LambdaTest’s integrations with popular CI/CD tools streamline the process of running visual regression tests as part of the continuous integration workflow.

Section 5: Analyzing Test Results

Visual regression testing generates valuable test results that need to be interpreted to identify visual discrepancies effectively. When running a test in LambdaTest, the platform captures screenshots of the web application in different browser and device configurations. These screenshots are then compared against the baseline images defined earlier. Here’s how to interpret test results and address visual issues:

1. Identifying Visual Discrepancies:

   – In the test results, LambdaTest highlights any visual discrepancies between the baseline images and the current screenshots.

   – Visual discrepancies are usually shown as red or marked areas, indicating where the changes have occurred on the web page.

   – Inspecting the discrepancies helps in understanding what visual elements have changed, such as colors, fonts, layout, or missing elements.

2. Prioritizing and Resolving Visual Issues:

   – Not all visual discrepancies are critical, so it’s essential to prioritize them based on their impact on the user experience.

   – High-priority issues may include broken layouts or missing content, while low-priority issues may be minor color variations.

   – Teams can create a bug triage process to categorize and prioritize issues based on their severity and impact on users.

   – Once prioritized, development and QA teams can work together to resolve the visual issues and ensure consistent user experiences.

3. LambdaTest’s Comparison Tools and Analytics:

   – LambdaTest offers advanced comparison tools and analytics that provide deeper insights into test results.

   – Users can view side-by-side comparisons of the baseline and current screenshots to understand the differences better.

   – The platform allows users to view changes pixel-by-pixel, making it easier to pinpoint exact visual alterations.

   – Detailed analytics help teams track the history of visual changes and monitor how the application’s appearance evolves over time.

Section 6: Integrating LambdaTest into Your CI/CD Pipeline

Incorporating visual regression testing into the CI/CD workflow is crucial to ensure that visual issues are caught early and don’t affect the production environment. The continuous integration and continuous deployment (CI/CD) pipeline allows teams to automatically run tests whenever code changes are committed. Here’s how to integrate LambdaTest into your CI/CD pipeline:

1. Importance of Visual Regression Testing in CI/CD:

   – CI/CD promotes rapid development and deployment, but it also increases the risk of introducing visual bugs.

   – By adding visual regression tests to the pipeline, teams can detect visual issues at an early stage and prevent them from reaching production.

2. Integration Process with Popular CI/CD Tools:

   – LambdaTest offers seamless integrations with popular CI/CD tools like Jenkins, GitLab CI, CircleCI, and others.

   – Integrating LambdaTest involves setting up test configurations, specifying test suites, and defining the browsers and devices for testing.

   – The integration allows teams to trigger visual regression tests automatically whenever new code is committed.

3. Automating Visual Regression Tests:

   – Automation is key to ensuring continuous monitoring of visual changes in a dynamic web application.

   – LambdaTest provides APIs and command-line tools that enable users to run tests programmatically and incorporate them into automated build processes.

   – By automating visual regression tests, teams can establish a robust feedback loop where issues are identified, resolved, and retested quickly.

Section  7: Troubleshooting Common Issues

Visual regression testing, like any other testing process, may encounter challenges. Addressing these common issues helps maintain the accuracy and effectiveness of visual regression tests. Here are some troubleshooting tips and solutions:

1. False Positives/Negatives:

   – Sometimes, visual discrepancies may be flagged as issues when they are harmless, leading to false positives.

   – On the other hand, actual issues might be missed due to minor variations, resulting in false negatives.

   – Adjusting the tolerance level and refining the test scripts can help reduce false positives and negatives.

2. Dynamic Content:

   – Websites with dynamic content may show visual differences, even when the functionality is working as intended.

   – Employ dynamic element locators and exclusion rules to exclude dynamic content from the comparison process.

3. Slow Test Execution:

   – Running tests on multiple browsers and devices may lead to longer test execution times.

   – Optimize test suites, use parallel testing, and leverage LambdaTest’s efficient test infrastructure to improve execution speed.

4. Limited Test Coverage:

   – Testing on a limited set of browsers and devices may result in missing critical visual issues.

   – Use LambdaTest’s vast browser and device coverage to expand test coverage and ensure compatibility across a broader audience.

Conclusion

Visual regression testing is a crucial aspect of web development that helps deliver a flawless user experience. By using LambdaTest, developers and QA professionals can efficiently identify visual discrepancies, prioritize and resolve issues, and continuously monitor their web applications for visual changes.

The integration of visual regression testing into the CI/CD pipeline ensures that visual issues are caught early in the development process, preventing them from reaching production and impacting end-users. With its advanced features and customizations, LambdaTest enables comprehensive testing across various scenarios, including geolocation and responsive testing.

Addressing common challenges and troubleshooting issues ensures the accuracy and effectiveness of visual regression tests. By embracing visual regression testing with LambdaTest, development teams can enhance their web development process, improve user satisfaction, and deliver high-quality web experiences. Start implementing visual regression testing with LambdaTest today to stay ahead in the competitive digital landscape.

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