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Visual Testing: A Beginner’s Guide

Shreya Bose, Community Contributor -

What is Visual Testing

Visual testing is a software testing technique that evaluates the visual appearance and behavior of a software application’s user interface (UI) or graphical user interface (GUI). Visual testing aims to verify that the application’s visual elements like colors, images, fonts, and layouts, are displayed correctly and consistently across different devices, operating systems, and browsers.

Why Should you Perform Visual Testing [with example]

Visual testing ensures that the user interface (UI) of the developed product appears as intended for users. It accomplishes this through several key benefits, including:

  • Identifying defects or issues in the UI interface
  • Detecting variations in the UI that do not match the baseline snapshots
  • Creating specialized visual test cases that cover functional points
  • Identify visual bugs on different browsers

Furthermore, visual testing provides an efficient and effective method for testing software applications, allowing testers to identify visual defects and inconsistencies that may negatively impact the user experience and usability of the application.

Take a moment to imagine something.

A new shopping website has been created. As with every site, the intention is to improve customer experience by letting customers purchase everything (from clothes to cookies) online.

Now, all automated tests show that the site is working perfectly, but once it actually goes live, things don’t work out so well. Customers tried to make a purchase by selecting items and entering their financial information, but couldn’t find a Checkout button when using a mobile browser. When investigated, it is found that the button is covered up by a text box because of the mobile device’s reduced screen space. This was not detected in the testing phase and then became a significant hurdle in user experience.

Visual Testing is the answer to such problems. It verifies that the software user interface (UI) appears correctly to all users. Essentially, visual tests check that each element on a web page appears in the right shape, size, and position. It also checks that these elements appear and function perfectly on a variety of devices and browsers. In other words, visual testing factors in how multiple environments, screen sizes, OSes, and other variables will affect software.

How to Perform Visual Testing?

Visual tests generate, analyze, and compare browser snapshots to detect if any pixels have changed. These pixel differences are called visual diffs (sometimes called perceptual diffs, pdiffs, CSS diffs, UI diffs).

For visual testing, QAs need –

  1. A test runner to write and run tests
  2. A browser automation framework to replicate user actions

Developers create code that replicates user functions, (typing text into a field, for example). At appropriate points in the code, they place commands to capture a screenshot. The first time the test code is executed, an initial set of screenshots is recorded – to act as a baseline against which all further changes will be compared.

After setting the baseline, the QA runs the test code in the background. Anytime a change is identified, a screenshot is captured. Then each screenshot is compared to the baseline image corresponding to that particular section of the code and the software. If differences occur between the images, the test is considered failed.

Once the test code runs completely, a report is generated automatically. A QA reviews all the images that have been diagnosed as changed from their baseline. Some testing tools actually generate reports that highlight the differences between baseline and final images, as detected after the test execution.

If these image differences are caused by bugs, developers can fix them and rerun the test to check if the fixes actually worked. If differences are caused by subsequent changes in the UI, developers will have to review the screenshot and update baseline images against which visual tests can be run in the future.

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How is Visual Testing Different from Functional Testing

Visual testing focuses on the appearance and behavior of the user interface whereas functional testing focuses on testing the functionality of the software application. Visual defects such as alignment, pixel to pixel comparison, rendering, layout, overlap, font change, responsive layout etc cannot be identified in functional testing.

Most software tests are designed to verify that various aspects of software functions are working as they are meant to. However, these tests don’t usually cover visual aspects of the software, which are extremely important from the users’ perspective.

In the example at the beginning of the article, functional tests would have shown that the website was working perfectly, including the Checkout button. But in the real world, the users of the website were facing a major issue and couldn’t execute one of the main functions the website was actually built for.

Visual testing fills gaps left by functional testing with regard to the visual side of things. In tandem with functional tests, it ensures that not only does the software work perfect, but it also looks visually on point.

Visual Testing vs Functional Testing

Visual testing and functional testing are two different types of software testing. Both types of testing are important in ensuring the overall quality of a software application.

Visual Testing

Functional testing

Visual testing focuses on the appearance and behavior of the user interface.Functional testing focuses on testing the functionality of the software application.
Visual testing aims to verify that the application’s visual elements are displayed correctly and consistently across different devices, operating systems, and browsers.Functional testing aims to verify that the application’s features and functionalities are working as intended.=

Understanding Manual Visual Testing

Manual visual testing refers to the process of manually inspecting and verifying the visual aspects of a software application or website to ensure that it meets the desired design and functional requirements. This type of testing is typically done by human testers who use their eyes to evaluate the appearance, layout, and behavior of the application or website.

During manual visual testing, testers will perform a series of tasks, such as clicking on buttons, filling out forms, and navigating through different pages, while paying close attention to how the application or website looks and behaves. They will check for issues such as broken links, missing images, incorrect font sizes or colors, and other visual defects that could impact the user experience.

Manual visual testing is an important part of the overall software testing process, as it helps ensure that the application or website is visually appealing, easy to use, and meets the expectations of end-users. It is often performed in conjunction with other types of testing, such as functional testing, performance testing, and usability testing.

Challenges in Manual Visual Testing

Manual visual testing can present a number of challenges, including:

  1. Human error: Since manual visual testing is performed by humans, there is always the possibility of human error. Testers may miss certain issues, or may misinterpret visual cues, leading to inaccurate results.
  2. Time-consuming: Manual visual testing can be a time-consuming process, particularly for complex applications or websites. Testers may need to manually check each page or screen, which can be a time-intensive process.
  3. Inconsistency: There can be inconsistencies in the way different testers evaluate the visual aspects of the application or website, leading to varying results.
  4. Difficulty in reproducing issues: If an issue is identified during manual visual testing, it can be difficult to reproduce and isolate the root cause of the issue.
  5. Limited scope: Manual visual testing may not be able to cover all possible scenarios and edge cases, leading to potential blind spots and missed defects.
  6. Costly: Manual visual testing requires a significant investment in terms of time and resources, particularly if a large number of testers are needed to perform the testing.

To overcome these challenges, organizations can consider using automated visual testing tools that can help reduce human error, improve consistency, and increase the efficiency of the testing process.

Understanding Automated Visual Testing

Automated visual testing is the process of using specialized software tools to automatically verify the visual appearance and behavior of a software application or website. Unlike manual visual testing, which is performed by human testers, automated visual testing is conducted using computer programs that can simulate the actions of a human user and evaluate the visual elements of the application or website.

Automated visual testing tools use algorithms to compare the expected visual appearance of the application or website with its actual appearance and can identify any discrepancies or defects. These tools can be used to test a wide range of visual elements, including text, images, colors, and layout.

Automated visual testing can help organizations overcome the challenges associated with manual visual testing, including human error, inconsistency, and time-consuming processes. It can also help organizations to achieve greater test coverage and identify defects that might be missed by manual testing.

Challenges in Automated Visual Testing

Automated visual testing, like any other type of automated testing, can also present its own set of challenges, including:

  1. Maintenance: Automated visual testing requires regular maintenance to ensure the testing scripts remain up-to-date and accurate as the application or website changes over time.
  2. Scripting: Creating and maintaining automated visual testing scripts can require specialized skills and expertise in programming languages and testing frameworks, which can be a barrier to entry for some organizations.
  3. False positives/negatives: Automated visual testing scripts can sometimes generate false positives or negatives, leading to incorrect results.
  4. Limited scope: Automated visual testing can only test what has been specifically programmed into the testing scripts, which can limit the scope of the testing and potentially miss important defects.
  5. Environment setup: Automated visual testing requires a stable and consistent testing environment, which can be challenging to set up and maintain, particularly for web applications that rely on third-party services or components.
  6. Cost: Implementing automated visual testing requires an initial investment in terms of time, resources, and tools, which can be a barrier for some organizations.

Visual Testing Tools

As previously mentioned, visual testing requires a test runner – to write and run tests. Test runners enable testers or developers to create code that reproduces user actions. Each test carries assertions defining a condition that will either pass or fail. Organize tests into blocks and put these blocks into one file that will be used to test a specific module or software function.

Once tests are written, use a tool like Selenium or Cypress to interact with the browser. They support visual tests and allow for the generation of screenshots of web pages.

Finally, one must have a tool for managing the testing process. Percy by BrowserStack is one of the best-known tools for automating visual testing. It captures screenshots, compares them against the baseline images, and highlights visual changes. With increased visual coverage, teams can deploy code changes with confidence with every commit.

Visual TestingWith Percy, testers can increase visual coverage across the entire UI and eliminate the risk of shipping visual bugs. They can avoid false positives and get quick, deterministic results with reliable regression testing. They can release software faster with DOM snapshotting and advanced parallelization capabilities designed to execute complex test suites at scale.

percy visual testing

Percy’s SDKs enable users to install them easily and add snapshots. Percy also integrates with CI/CD pipelines and source code management systems to add visual tests to each code commit. After tests are initiated, Percy grabs screenshots, identifies visual changes, and informs the testing team of all changes. Then, testers can easily review visual diffs to decide if the changes are legitimate or require fixing.

Visual Testing: A Beginner’s Guide

By incorporating visual testing into the testing process, testers will be able to deliver visually perfect applications quickly and consistently. It also helps them create websites that maintain visual consistency across the entire UI by offering comprehensive visual reviews and accurate results. Looks do matter, especially when users have thousands of other websites to choose from. Make your site look good and work well, and you will keep your visitors happy.

Advantages of Visual testing

  • It is user-friendly: Visual testing is easy to understand and execute, making it a user-friendly approach to testing.
  • It catches UI-related bugs: Visual testing can identify bugs related to UI design and behavior, such as incorrect positioning of elements, color contrast, and visual alignment issues.
  • It saves time: Visual testing can save time by automating the process of verifying the visual appearance of an application, allowing testers to focus on other types of testing.
  • It helps improve user experience: Visual testing can help improve the user experience by ensuring that the application looks and behaves as expected.
  • Helps identify cross browser visual issues

Disadvantages of Visual Testing

  • It is not comprehensive: Visual testing is limited to the verification of the GUI and may not identify functional or non-GUI related issues in the application.
  • It requires specialized skills: Visual testing requires testers to have specialized skills and knowledge of design principles and visual elements.
  • It can be time-consuming: Visual testing can be time-consuming, especially when it involves manual testing.
  • It may not be suitable for certain applications: Visual testing may not be suitable for applications that do not have a GUI or have a limited graphical interface.



Visual Testing

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