Regression Testing is used to prove that any system changes do not impede existing features and/or code structure. It is common for developers to include these tests as part of almost every test suite in software development.
When they change or add any section of code, it is always possible to unintentionally disrupt something that was previously working fine.
When these disruptions might affect any visual aspect of the software, testing for any possible errors is called visual regression testing. These tests check that code changes do not break any aspect of the software’s visual interface.
These tests check what will be seen after any code changes have been made. Screenshots are taken and compared with how the image looked before the code changes were made.
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For an example of why visual regression testing is needed and how it works, let’s assume you open a web app and try to click on a button, but you can’t because an advertisement is covering most of the button. You will be irritated by not being able to conduct this action and will probably leave the app.
This sort of issue is called a visual bug. It is an error that affects your experience of that software.
Visual regression testing is designed to find these bugs so that they can be fixed before users can access the software with the errors. Because users access the software on a variety of computers, tablets, and mobiles with different screen sizes and possibly with differing zoom settings, it is easy for a small change to cause an error in the visual display for some of these hundreds or thousands of different screen sizes, settings, and resolutions.
Having a method to check on any “code-to-pixel” conversations quickly and easily on all the possible different device-browser-operating systems needs to be a part of any development project.
Visual regression testing tools capture screenshots of the current user interface and compare them with the original screenshots for historical differences. It checks to see if the web page still looks the same across various browsers even after changes to the code have been made.
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The importance of visual design
Ensuring the visuals look good is vital because visual design shapes the user experience in so many ways, including:
- Great visual designs help to build trust and credibility.
- Reinforces brand image.
- Affects legibility.
- Forms a visual balance on the screen.
- Guides the users towards actions.
- Persuades the eye to shift its attention towards certain page elements.
Three different visual testing methods are generally followed.
Create Dedicated Visual Tests
This is the most recommended method because it gives you full control over visual validation. By using this approach, you can write tests without a great deal of effort, but you do need to write the tests from scratch and that can take up some considerable time.
Insert Visual Checkpoints in Existing Functional Tests
You use existing tests for confirming the functionality of the application, and you just add some visual checks between the tests to confirm the pages. This method limits your test coverage but it’s a quick way of inserting visual tests.
Insert Implicit Visual Validation to the Existing Testing Framework
With just a few lines of code to write, this method is quite easy to implement. However, it is limited because you can’t validate specific components within the framework.
Manual vs Automated testing
Although manual testing can be slow, expensive, and error-prone, sometimes it is not possible to capture the correctness of every scenario. One of the major advantages of manual testing is that a human can look outside the scope of the test. They might find other cosmetic bugs and anything that looks incorrect.
Manual Testing Steps:
- Start by capturing each known good baseline screenshot.
- When completed, take another set of screenshots from the latest version.
- Manually compare the new screenshots to the original to find any visual bugs.
Automated testing offers long term cost efficiency, greater speed and accuracy excluding human error delivers pixel-perfect visual tests, are reusable & transparent contributing to automatic reports that are easily accessible by anyone in the team.
There are 4 steps involved in Automated Visual Testing:
- Step 1: Drive the application to evaluate and capture screenshots.
- Step 2: The automated tool compares these screenshots against the baseline screenshots.
- Step 3: Once the tool obtains the results of the image comparisons, it generates a report that highlights all the differences found.
- Step 4: The tester reviews the report and checks each difference to see whether it is a bug or a valid change (false positives). Based on the results, the baseline images are updated.
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Like all technology, automated visual regression testing is faster and potentially more accurate, but is only ever as good as the scope it is working to. A human can look outside the automated scope and potentially pick up errors missed by automated testing.
A mix of automated and manual testing is often the best solution.