Visual regression testing is used to verify that an application, website, or other software behaves and looks as expected. It also verifies that no changes have been made unintentionally in the visual appearance and functionality. This involves comparing an application or website’s baseline and current versions to check for visual differences.

During Visual Regression Testing, images of an application or website are captured, compared, and highlighted using specialized tools. The two versions may differ, indicating that an application’s layout or appearance has changed.

This is usually used with other types of testing, such as Functional Testing and Usability Testing, to verify that websites and applications work properly and meet quality standards. This is useful when the appearance of an application or website is important to its user’s experience or when frequent changes need to be monitored.

This blog will discuss in-depth visual regression testing and how to perform visual regression testing with Selenium. 

What Is Visual Regression Testing?

By comparing screenshots taken before and after code execution, visual regression testing can ensure that code changes impact the user’s experience. It is also known as Visual Testing or visual snapshot testing.

Visual testing is a way to verify the suitability of the visual aspects of the interface of an application. Visual testing or visual validation are other terms we can use. This quality assurance measure aims to ensure that the front end of an app displays the correct data and content.

Regression Testing is a term that you may not be familiar. It ensures that any changes to software you make do not cause problems with elements that previously worked well. This testing is a visual test that ensures any software changes don’t lead to style issues.

Visual regression testing tools usually take screenshots of the most recent user interface and compare them with the original screenshots. The website should still render exactly as expected despite several modifications. The web page should look and function the same on various browsers.

Why Perform Visual Regression Testing?

Today, applications are evolving to meet customer needs. It is important to maintain the functionality and layout of the application across different browsers.

Visual testing is now a crucial part of the process, especially since most companies have adopted Continuous Integration.

The user interface must look good across various devices, browsers, operating systems, and screen resolutions. It only takes a small UI error to result in excessive revenue losses. Customers are unlikely to use a banking application with many bugs for security reasons. Even if the application is not as sensitive as banking, users will still leave it if they find it inconvenient or annoying.

Visual discrepancies can be easily detected when the QA team performs visual regression tests in earlier SDLC phases and developer testing. Businesses can also use this approach to save time and resources they could otherwise devote to other scaling methods. It doesn’t really matter how perfect your application is. It doesn’t matter how flawless your application is if you don’t provide a great user experience. Visual testing is crucial to quality control, whether about UX or UI.

Visual regression testing is also important because high-quality designs give a company more credibility and trust by enhancing its brand image. Visual testing is useful in many areas, including web and mobile apps, customer systems like airlines, banking, travel and airline sites, and marketing websites.

A company must also find a way of affording to let expensive visual bugs slip into production. Functional testing is a way to validate data inputs and outputs. Even though the most important part of functional testing is to uncover visual bugs, it does not cover all bugs. Even the best-tested apps can have bugs that are not visible.

Benefits Of Visual Regression Testing Using Selenium 

Visual regression testing has many benefits, including improved user experience, cost savings, high-quality products, and more.

  • One test will check for labels, font types, alignment, color, layout, and links.
  • Test analysts can spend more time on interpretation and solving real-world problems.
  • Displays and small-scale UI variants.
  • Comparing visual elements across multiple browsers.
  • It encourages the user’s attention to specific elements of the page.
  • Increase the value of automated functional checks.

What Are The Different Methods Of Visual Regression Testing?

Visual regression tests compare screenshots of the interface just before a change is implemented to another screenshot. The test engineer reviews the differences and then takes the process forward.

Check out the different types and processes for visual regression testing.

Visual tests are in charge of creating, analyzing, and comparing screenshots. They check pixels. A framework and test runner are in place. A framework is used to replicate user actions as they browse. This involves simulating user actions and taking snapshots for a long time to compare the changes against a benchmark. Once the benchmark has been set, QA will execute the test code.

After the test is completed, a report will be generated automatically based on which visual regression testing tool you are using. Developers can run tests and repairs to test the effectiveness of fixes in the event of an issue. Developers may also need to update baseline images depending on the requirements to ensure future visual tests.

i) Manual Visual Testing: The name implies that developers perform visual regression testing manually without using automated testing tools. This is done by scanning the pages for defects and checking them during every release.

This method is especially useful in early development phases, allowing for exploratory or Ad hoc testing. Using a manual testing approach for an entire application is slow and cumbersome. Another major disadvantage is the human error factor.

ii) Layout Comparison: This approach compares size and position instead of pixels. The test will fail if an element’s size or position changes.

iii) Pixel-by-Pixel Comparison: This method compares the two screenshots at a pixel level. It alerts the tester in case of discrepancies. Pixel-by-pixel comparisons and pixel mismatches are enough to flag any possible issues.

The downside is that it may also cover cases irrelevant to usability and almost invisible to the naked eye. Anti-aliasing and rendering issues, as well as differences in margin, are some of the most common. The test engineer can manually filter out false positives.

iv) Structural Comparison: This method compares the DOM to determine HTML markup. If they are present, the test fails.

v) Visual AI Comparison: This type of visual testing uses ML and AI to take two images. It can be used on dynamic web applications without a baseline. Computer vision can see the interface just like humans. This method can save time by preventing false positives. Testing dynamic content is another capability. Problems can also be flagged only in regions that have unexpected changes.

vi) DOM-Based Comparison: This approach is based on a layout comparison. First, compare UI elements structurally. Next, check their sizes and locations. The Document Object Model is used to compare the state of a document before and after a change. This brings DOM code alterations into focus. On the other hand, the results of tests can be faulty. Testers must, therefore, review them slowly and carefully to avoid visual bugs from escaping.

Steps To Perform Visual Regression Testing Using Selenium

With Smart Testing, you can perform Visual UI Regression testing with just one click using the LambdaTest Platform. Here is a  step-by-step through the process of performing Visual Regression tests.

  • You need to have a basic understanding of Selenium automation testing and WebDriver. 
  • Go to the LambdaTest Smart UI and log in with your details.
  • Now, you have access to the hub for your Selenium remote connection. 
  • Copy the username and LT access key from your dashboard. 

Step 1: Create a SmartUI Project

First, create a new project for the application. This project will be used to combine all of your builds that are running on it. Follow these steps to create a SmartUI Project:

  • Go to the Projects Page
  • Click the New Project button
  • Choose Web as the platform for your Selenium test.
  • Add the name of the project and the approvers who approved the changes. Tags can be added for easy navigation or to filter the results.
  • Click on Submit.

Step 2: Configure the Test With Selenium Desired Capabilities

When you have created a SmartUI Project, you can also generate screenshots using automation scripts. To successfully generate screenshots, follow the steps below. 

i) Please clone the following sample Github repo

git clone https://github.com/LambdaTest/smartui-node-sample

ii) Follow the instructions in the README.md to set up your LambdaTest credentials.

iii) Edit the test suite to include only your needed capabilities.

  • The code must be placed below the segment of the selenium script we want to screenshot test.
  • Installing dependencies and executing tests.
  • You can view the results of the tests at LambdaTest.

Conclusion On Visual Regression Testing With Selenium

Visuals are a key factor in sales and success. It is, therefore, important to prioritize visual regression testing, regardless of an organization’s industry. Visual testing can change the game for any organization if the teams adopt the right approach. If you’ve got the right tool at your disposal, you can improve your visual game.

LambdaTest is a AI powered test orchestration and execution platform that is a pioneer of visual testing that can be performed with just one click to find visual UI regression issues. Smart testing allows you to compare images and detect visual deviations in text, layouts, colors, sizes, paddings, element positions, etc.

With Selenium, Cypress, and multiple languages like Java, Node.js, and C#, you can automate visual testing and deliver visually flawless software applications. Parallel testing allows for a drastic reduction in test execution times. You can integrate seamlessly with the entire CI/CD technology stack.

LambdaTest Smart UI Cloud (visual regression testing cloud) has other features.

  • Visual testing options include largeImageThreshold (large image threshold), errorType (error type), ignore, transparency etc.
  • Leverage Webhooks for even more intelligent testing.
  • LambdaTest offers a variety of options to reduce the flakiness of the output from your compressed screenshots.
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