How to Perform Advanced Visual Testing with Selenium?

Automated visual testing is often considered a difficult task in the software industry. However, this is just a misconception. Due to this false impression, people fail to capitalize from the easy implementation of visual testing.

Visual testing caters the need to verify the Graphical User Interface (GUI) of an application from the users’ perspective.  The process helps in identifying bugs related to font, layout, etc., so that they can be fixed before being used by end-users. In addition, it overcomes the verification challenges associated with conventional testing tools, especially in case of sites having graphical functionality, including charts, dashboards, etc.

With the advancement in technology, there has been a rise in the number of web browsers, operating systems, responsive designs, etc. This has eventually made visual testing quite complex. However, today there are a number of open source and professional tools to handle this, making the life easier than before.

Automating a visual test will ensure optimal performance of each page. It checks each element and tells you if any of them are not rendered properly. This happens each time you run the test. Moreover, you can extend this to each browser, OS, design, and more.

In other words, an automated visual test takes you one step forward towards continuous delivery.

Solution 

Automated visual testing is quick and easy by using an existing solution. Each tool follows a similar workflow. However, there are some variations.

1. Run the application being tested and take a screenshot.
2. Compare the screenshot with the standard image.
3. Note the differences.
4. Update the standard image as and when required.

Example

Consider working with a Selenium WebDriver to test an application on the Internet. Assume there is a menu bar along with a button that shifts 25 degrees on either side each time the page loads.

Once you have started the Selenium Standalone Server, you need to create another file. You need to include the necessary libraries and configure Selenium to get connected to the standalone server.

You can get the driver object to interact with the browser, as shown below.

The above-mentioned commands allow us to mention the areas on which we want to perform visual testing.

Consider the following body page.

You can use the assert command to ensure there are no visual changes after running the test again. The Webdriver CSS takes the screenshot each time the script is run. The first shot acts as a baseline and is compared with the subsequent shots. If there is a mismatch, then the script will fail. The baseline needs to be updated if the script keeps on failing.