Software Testing – Visual Testing

Visual Testing is also called Visual UI Testing. It validates whether the developed software user interface (UI) is compatible with the user’s view. It ensures that the developed web design is correctly following the spaces, sizes, shapes, and positions of UI elements. It also ensures that the elements are working properly with various devices and browsers. Visual testing validates how multiple devices, browsers, operating systems, etc., affect the software.

Features of Visual Testing:

• Deliver a consistent user interface.
• Rapid and responsive testing.
• Continuous visual regression testing.
• Test on every commit.
• No test scripts are needed.

This article focuses on discussing each of these topics-

1. Visual Inspection System.
2. Working of Visual Testing.
3. Why Visual Testing?
4. Why Functional Testing Can’t Cover Visual Testing?
5. Visual Testing Methods.
6. Types of Visual Testing.
7. Tools for Automated Visual Testing.
8. Advantages of Visual Testing.
9. Disadvantages of Visual Testing.

Let’s start discussing each of these topics in detail.

Visual Inspection System

Automated Visual Inspection or Visual Inspection is the process of analyzing the products for the entire control of the product quality. Here, the software is developed with an image capturing algorithm and it captures the images for checking the quality of the product which matches with our requirements as is mentioned by the client or business team. It reduces the manual working and provides the best outcome regarding the result. The rate of checking the product is speed and efficient. It ensures the correctness of the product.

Working of Visual Testing

Visual tests generate, compare and analyze browser snapshots to detect if any pixels have changed. These pixel’s differences are called visual pixels. 

Steps in Visual Testing:

• The Quality Analyst or the tester runs the developed code to test the web application’s user interface part. 
• Initially, it will record the screen as snapshots. It acts as a baseline with which the further test results will get compared.
• After that, the QA runs the code in the background and it will take or record the snapshots of those running codes. 
• Now, it will start comparing with the baseline snapshots.
• If changes are found among those snapshots then the test is considered as failed.
• If no changes are found then it will be tested positively. 

Process in Visual Testing

Some visual testing tools will generate reports where the differences in the snapshots are captured. It finds where actually the snapshots get differed. Also, it generates the report for successful test results.

• If these image differences are caused by errors, developers can fix them and return 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.

Why Visual Testing?

Visual testing is done because visual errors happen more frequently than one might realize. Some of the reasons for doing visual testing are-

• It verifies or ensures that the developed product UI appears as expected to the users. 
• It helps in evaluating the defects in the UI interface. 
• It correctly detects the variations in the UI which is not relevant to the baseline snapshots. 
• It helps to create dedicated visual test cases and covers the functional points. 
• Visual testing allows the tester or Quality Analyst to evaluate the test cases visually which is easier to carry out.

Why Functional Testing Can’t Cover Visual Testing?

Visual bugs are rendering issues. Rendering validation is not caught by functional testing tools. Functional testing measures functional behavior. But, if there is a requirement to check the functionality of the website, in that case, function testing works properly and ensures the same. If the visualization of the website is very messy as not expected then it will not be detected by functional testing.

Example: While creating a website the submit button is placed at the center but after the entire process by mistake if it is moved to the right side of the browser page then during the functional testing it will not catch or find that defect that the submit button is wrongly placed. Because it checks whether the submit button functionality is working properly or not. Here, it can’t cover the visual testing.
In the case of visual testing implementation, it compares the various snapshots with the baseline snapshots and will detect the defect that the submit button is wrongly placed. It helps the tester to find the defect with minimum test runs.

Visual Testing Methods

Below are some of the methods for Visual testing:

1. Create dedicated visual tests: In this, the tester will write the test cases for different scenarios. Here, moderate efforts of writing test cases will only be required. Writing the test cases from scratch is important and it needs some significant time to write the accurate test cases. 

2. Inserts Visual Points in existing functional tests: In this method, the tests for validating the functionality of the application are already present and just some visual checks need to be added between these tests to validate the pages. Of course, this method limits your test coverage but it’s a quick way of inserting visual tests and taking the benefit from the existing functional testing code.

3. Insert Implicit Visual Validation to the Existing Testing Framework: This method is very easy to implement as it requires only a few lines of code. However, it suffers from the limitation that one can also do generic validation in this case. One can’t validate specific components in the framework. 

Types of Visual Testing

Below are the two types of visual testing:

1. Manual Visual Testing: In manual visual testing, the tester will manually check the layout and user interface elements on the web page. Here, the tester has to manually take the snapshots or screenshots to compare these snapshots with the baseline snapshots to detect the differences and confirm them to the team.

Another effective way to do manual testing is to use a component explorer. In this, you the tester define the test states, use explorer to select a state and component, and check it on the screen. One such tool is React Storybook where one 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.
• Manually compare these screenshots (baseline vs current) to figure out the visual bugs.

2. 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 and these are faster than manual tests and more accurate as they can exclude human errors and deliver pixel-perfect visual tests, they are reusable and transparent as they offer automatic reports that are easily and readily accessible by anyone in the team.

• 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.

Tools for automated visual testing

The following are some of the tools for automated visual testing:

Code-Based automated visual testing (Open Source Tools):

1. Specter:

• Specter is the automated visual regression testing framework. 
• After the web page is created, each individual component will be checked whether it is rendered properly or not.
• Specter will capture screenshots of the elements matching the selectors specified, at all the screen dimensions desired. 

2. Needle:

• It checks that visuals like images, layouts, buttons, CSS, SVG, etc., are rendered 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.

3. Gemini:

• It checks the visual appearance of the web page. Here, it tests the web page separately.
• It includes some of the CSS properties while checking the web pages with correct elements and their position.
• It gathers the CSS test statistics.
• Some of the rendering features for images are not supported.

4. Pix-Diff:

• It is developed to compare the screenshots of the developed web pages.
• The image comparison is carried out in three ways- Pixel-by-Pixel, Perceptual, and context.
• It ensures that the part of the image is missing.
• It is used to check the low-frequency images.

5. FBSnapshotTestcases:

• It takes a UI View or layer and uses the necessary UI kit to generate the automated image snapshots of its content.
• It creates the reference image and compares it with the actual image of the generated code.
• One pixel change will lead to the failure of testing.

Configuration – Based automated visual testing (Open Source Tools):

1. CSS visual test: It checks the correctness of the CSS properties with the image generated.
2. VIFF: It finds visual differences between web pages in different environments such as developing, staging, production and browsers.
3. GreenOnion: It checks only the UI part of the website and ensures that the designs, views, etc., are made correctly.
4. Galen Framework: It is used to test the layout of the web application from various devices. 
5. CSSCritic: It is to check the current layout of the web page constantly against the reference image generated early.
6. Baskstop JS: It checks the entire layout or part of the layout of the UI and compares it with DOM screenshots.

Advantages of Visual Testing

1. Increased quality of code and UI.
2. Rapid bug detection.
3. Control of Views on different devices and browsers.
4. Easy to implement.
5. Fast implementation.
6. Automation.
7. Reduction of Code.
8. Efficient feedback of results during testing.

Disadvantages of Visual Testing

1. It can not detect smaller defects.
2. It requires the minimum skills to implement. It is a little difficult for beginners.
3. Sometimes, video recording is not so clear.
4. Possibilities of containing the detect even though testing has been implemented.
5. Tests only the visible or light surface.