Visual Regression testing or Visual validation testing in software is a quality assurance activity of verifying if the visual aspects of the application’s user interface seem appropriate to the user. It is also known as Visual Validation Testing. It aims at verifying if the correct data and content are getting displayed at the application’s front end.
Additionally, it also validates the layout and appearance of each visual element present on the user interface and the whole UI itself.
Since we at BugRaptors always aim to meet the highest benchmarks of quality as a software testing and quality assurance service provider, we believe it is necessary to keep our audience informed of the most comprehensive test procedures.
In this blog, we will aim to highlight the concept of visual validation testing sharing insights on its importance, methods, and processes involved. Besides, we will even share a list of the best available tools that can be used to complement visual validation testing goals.
Importance Of Visual Validation Testing
No matter how correctly the functionality of your application is working, it won’t be of use to the customer unless it can provide a good user interface and user experience.
These days, we not only talk about UI (User Interface), but we also focus a lot on UX (user experience). When we are targeting to deliver a better user experience, then visual testing becomes much more important because the more appealing visual design can be perceived as more usable to the user.
Visual Testing Methods and Processes
As developers or testers, we often work on testing the functionality of the applications. Either through manual or some automated tool, we check if the application is working as expected. Such functionality testing is very important to ensure the smooth working of the application.
However, if we add visual testing to this, then it would improve the overall testing significantly. Thus, this testing is often done in combination with functional testing.
There are several testing methods and processes to meet the challenges of visual testing of applications over wide configurations. There are also a lot of tools available to support visual validation testing. Generally, there are two main approaches followed for visual validation testing i.e. Code-based, and Configuration based. The visual testing tools are also categorized based on these two approaches.
It can be done manually or in an automated manner. Due to certain challenges involved, it can neither be fully manual nor fully automated. Generally, a combination of manual and automated approaches is preferred.
Manual Visual Testing
Software companies are faced with two options to perform visual testing i.e. Manual testing or Automated testing. Let’s see Manual visual testing in detail.
Although manual testing can be slow, expensive and error-prone, due to the subjective nature of the interface design, it is often not possible to have an automated test to capture the correctness of every scenario. So, at times we need to choose a balance between Manual and Automation testing.
Also, one of the major advantages of manual testing by a human being can look outside the scope of the test. An automation test can only capture the issue that is within its scope, but in a manual test, a human tester can also spot other cosmetic bugs and other things that look incorrect on the UI. Since manual tests are closer to real-life user actions, they can capture the layout bugs and design issues that are generally uncovered when a real user interacts with the application.
You can go for manual testing at the early stages of the application development when your UI is unstable. It is also helpful for ad-hoc testing when you need to have quick on-the-spot check-ups.
In manual visual validation testing, the tester has to manually check the appearance and layout of the visual elements. This may involve taking current screenshots and then manually comparing them against the baseline screenshots to identify any gaps.
Another effective way to do manual testing is to use a component explorer. In this, you define the test states, use explorer to select a state & component and check it on the screen. One such tool is React Storybook where you can develop UI components in isolation. Through this method, a tester can run a manual test of a component, check how it renders and see if it is working fine or not.
Manual Testing Steps:
Browse through the app and capture the known good baseline screenshots.
At a later point, take another set of screenshots from the latest version of the app.
Now, manually compare these screenshots (baseline vs current) to figure out the visual bugs.
Automated Visual Testing
Automated visual testing is a way to automatically verify if a user interface visually appears as intended. The benefits of automating visual tests are that they offer long-term cost efficiency, are faster than manual tests, are more accurate as they can exclude human errors & deliver pixel-perfect visual tests, they are reusable & transparent as they offer automatic reports that are easily and readily accessible by anyone in the team.
Some of the limitations of automated visual testing are that there can be large upfront expenses and you will need to spend significant efforts in test maintenance to accommodate every change. In automation testing, the scope is narrower unless screenshot testing is in place. Also, there is a steep learning curve as the organizations take time to learn about automation testing tools.
To go with automation would be a good choice if you are required to perform regression visual testing to deal with frequent changes happening to a stable UI. Automated testing also helps in a great visual screenshot comparison.
Automated screenshot comparison offers a great degree of precision in visual testing and increases the ROI. The automated screenshot comparison can capture those bugs that are impossible to get detected with human eyes and manual comparison. It is also helpful in the end-to-end testing for complex user stories. There are a wide variety of open source and commercial tools available for automated testing.
Best Visual Validation Testing Tools
Code/Script Based Open-source & Free Tools
PhantomCSS takes screenshots captured by CasperJS and compares them to baseline images using Resemble.js to test for rgb pixel differences. PhantomCSS then generates image diffs to help you find the cause.
Screenshot-based regression testing can only work when UI is predictable. It's possible to hide mutable UI components with PhantomCSS but it would be better to test static pages or drive the UI with faked data during test runs.
FBSnapshotTestCase is renamed as iOSSnapshotTestCase. A “snapshot test case” takes a configured UI View or CA Layer and uses the necessary UI Kit or Core Animation methods to generate an image snapshot of its contents.
IOSSnapshotTestCase creates a reference image on the predefined path and compares it to the actual image generated from the code. only a 1-pixel change can be a failed test case. IOSSnapshotTestCase is helpful while you are working with multiple UI and when you mistakenly change your UI.
Gemini is a utility for regression testing the visual appearance of web pages.
Gemini allows you to:
Test separate sections of a web page
Include the box-shadow and outline properties when calculating element position and size
Ignore some special case differences between images (rendering artefacts, text caret, etc.)
Gather CSS test coverage statistics
Gemini was created at Yandex and is especially useful to UI library developers.
Needle is a tool for testing your CSS and visuals with Selenium and nose.
It checks that visuals (CSS/fonts/images/SVG/etc.) render correctly by taking screenshots of portions of a website and comparing them against known good screenshots. It also provides tools for testing calculated CSS values and the position of HTML elements.
Rspec-page-regression uses PhantomJS to heedlessly render web page snapshots, by virtue of the Poltergeist driver for Capybara. You can also use the Selenium driver to test against real browsers. Rspec-page-regression is tested on ruby 1.9.3, 2.1.0, and jruby
Configuration Based Open-source & Free Tools
BackstopJS automates visual regression testing of your responsive web UI by comparing DOM screenshots over time.
layout settings for print and screen
scenario display filtering
reference, test, visual diff inspector
cool scrubber thingy
Integrated Docker rendering -- to eliminate cross-platform rendering shenanigans
Render tests with Chrome Headless
Simulate user interactions with Playwright or Puppeteer scripts
Plays nice with CI and source control
Run globally or locally as a standalone package app or require('backstopjs') right into your node app
Incredibly easy to use: just 3 commands go a long long way!
Make continuous deployment safe by comparing before and after webpage screenshots for each release. Depicted shows when any visual, or perceptual differences are found. This is the ultimate, automated end-to-end test.
A local command-line tool for doing perceptual diff testing.
An API server and workflow for capturing webpage screenshots and automatically generating visual, perceptual difference images.
A workflow for teams to coordinate new releases using pdiffs.
A client library for integrating the server with existing continuous integration.
Built for portability; server runs with SQLite, MySQL, behind the firewall, etc.
Need help aligning with accessibility testing? Check our suggested tools to keep things streamlined!
Read Here: Top Accessibility Testing Tools for Web Applications
3. CSS Critic
CSS Critic is a lightweight tool for regression testing of Cascading Style Sheets.
One picture might say more than 1000 words:
For background information watch the screencast or if you feel like playing around have a look at the runnable instance. This example project helps you get started with your own setup.
Your web stack should be fully testable. CSS Critic closes the gap in front-end testing and makes HTML & CSS testable - no more broken UI. For example, make it supervise changes to your project's responsive style guide so you know things are looking good.
How is it different to the other tools out there?
We believe that your UI will change often enough that a lightweight process for managing changes (near-instant feedback, anyone?) is more important than a heavy-weight one which could offer tighter control. Also, CSS Critic aims at bridging the gap between user experience (UX) people and (UI) developers. You probably won't find any easier way of sharing your UI tests than as the simple web page that CSS Critic basically is. And don't feel put down by the "CSS" bit, you may throw anything at it that can be converted into a simple image.
Grunt and Grunt plugins are installed and managed via npm, the Node.js package manager. Grunt 0.4.x requires stable Node.js versions >= 0.8.0.
Before setting up Grunt ensure that your npm is up-to-date by running npm update -g npm (this might require sudo on certain systems).
Find visual differences between web pages in different environments (developing, staging, production) and browsers.
Viff runs on selenium sever. You can easily set up selenium server using wdm.
$ npm install wdm -g
$ wdm update --standalone // install selenium and web drivers
Then install viff command line.
npm install -g viff
Checkout viff-examples repository for more examples, including:
Tiny CSS difference
Using Viff Server (beta)
Best for mobile testing teams.
Kobiton’s scriptless automated Visual Testing solution offers the most comprehensive mobile Visual Validation and Visual UX Testing solution.
Kobiton is a mobile testing platform that offers the most comprehensive mobile Visual Validation and Visual UX Testing solution.
It is built to optimize mobile UI and UX by finding visual bugs. It catches both visual and functional issues that would have otherwise gone unnoticed.
It offers manual and automated testing for mobile apps on real devices, in the cloud or even on-premise.
When you use Kobiton, you get instant access to over 350 real devices, and your own private cloud or local lab.
Why should we use Kobiton as a Visual testing tool compared to its competitors?
Kobiton’s Visual Testing solution has been built from the ground up to support mobile teams. With an intelligent AI at the core, Kobiton goes above and beyond just pixel-by-pixel comparisons offered by competitors to ensure users deliver picture-perfect applications across all devices and screen resolutions.
On top of that, Kobiton’s strive for innovation has led to entering the world of Visual UX Testing by capturing the essence of what makes an app beautiful and offers recommendations to its users to enhance the mobile application’s user experience.
With intelligence combined with innovation, Kobiton’s scriptless automated Visual Testing solution offers the market’s most comprehensive (Visual Validation + Visual UX Testing) and user-friendly solution for mobile testing and development teams.
Free Trial: Available
Start-up plan – $500 / year – For teams who need quick access to real devices
Accelerate – $2000 / year – For teams who need to quickly ramp up test automation
Scale – $8000 / year – For teams who need continuous testing & wide market coverage
Best for desktop and web-based applications.
Applitools offers “Applitools Eyes,” which is a Cloud Service for Automated Visual UI Testing of Web, Mobile and Desktop applications.
- It validates you’re the UI’s visual output across different operating systems, browsers, screen sizes, devices etc.,
- It supports full page screenshots, page layout matching, cross browser testing, and many more.
- It supports all major automated testing frameworks and languages including Selenium IDE, Selenium, Cypress, WebdriverIO, Protractor, Testcafe.
This tool integrates with the DevOps process and lets you easily create visual test cases to go into your CI/CD pipeline. Further, it gives you the ability to create custom visual reports for easy readability.
Free Trial: Available
3. Percy (Browser Stack)
Best for web-based applications.
Percy by Browser Stack is an automated visual review platform built for teams who are looking to run automated visual validation tests.
- It allows you to design, develop, and deliver software. It supports responsive visual testing, smart visual regression testing, and cross-browser testing.
- Its “pixel by pixel diffs” technology finds the smallest changes in your UI.
- Its “responsive diffs technology” allows you to test your UI across all screen widths.
- Its snapshot stabilization technology minimizes false positives.
- It by default freezes animations, and manages custom fonts.
Free Trial: Available
Pricing: $99 / month (billed annually)
4. Lambda Test
Best for image-to-image comparison.
Lambda Test comes with a Smart Visual Testing feature that allows teams to test and compare two image layouts to find out the differences between them. Lambda test smart image-to-image comparison technology allows you to find minimal visual bugs easily by simply uploading screenshots (baseline image and comparison image) and running the test.
Free Trial: Available
Live – $15 / month (billed annually)
Web & Mobile Browser Automation – $99 / month (billed annually)
Web Automation – $158 / month (billed annually)
Cross Browser Testing visual testing ensures that visual bugs don’t slip through to your customers. Its automated screenshots features make every mobile layout perfect. It allows you to do real device testing for visual testing on the cloud platform. It fits right inside your CI process with integration with CI tools like Jenkins, GitHub and much more.
Full Page Screenshots
Free Trial: Available
Live Testing – $ 29 / month(billed annually)
Unlimited Testing – $ 100 / month(billed annually)
Enterprise – Contact support
Chromatic helps make UI components consistent. It takes pixel-perfect screenshots of real rendered code, styling, and assets. Every commit to the repository is automatically tested for visual changes in the cloud. It can be integrated with GitHub, Circle CI, GitLab, Bit Bucket, Travis, Jenkins, Code Ship and more.
Free Trial: Available
Starter – $149/mo
Standard – $349/mo
PRO – $649/mo
7. Screener by Sauce Labs (Sauce Visuals)
Screener allows teams to test their user interface (UI) across multiple browsers, operating systems, and devices. It automatically detects visual regressions across your UI and spot inconsistencies. It compares both screenshots & DOM snapshots to show changes.
There are a number of automated visual regression testing tools available on the market today. Choosing one may depend upon your needs and budget, as well as what you want to accomplish with it. For example, if you’re looking for a tool that can be used especially for mobile testing teams, then Kobiton is the option for you. If you are looking for a tool to handle desktop or web applications Percy from Browser Stack and Applitools might be right up your alley.
Test Wisely! Good Luck!
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