Why use headless in Selenium?
Selenium, a widely used automation testing framework, has evolved with various capabilities to meet the needs of modern web application testing. One significant advancement in Selenium‘s toolkit is the advent of headless testing. In this article, we’ll delve into headless testing and its benefits and limitations and provide some history behind it.
Table of contents
- Understanding headless testing
- History of headless mode
- How to do headless testing
- Headless mode benefits
- Headless mode limitations
Understanding headless testing in Selenium
Headless testing involves executing automated tests on web applications without a visible graphical user interface (GUI). Firefox and Chromium-based browsers support using headless mode.
In traditional testing, a browser is launched, and actions are performed with the GUI visible to the tester. However, headless testing operates behind the scenes, executing the test scripts in the background without rendering the web page.
History of headless mode
It all started with Chrome 59 in 2017. The new feature was called:
“running Chrome without Chrome!”
That meant you could pass the
--headless flag in your Selenium tests to run tests in non-GUI mode.
What the team at Google did to accomplish that was to have two separate, alternate browser implementations as part of the same Chrome binary. That meant that any time one wanted to run tests in headless mode, the headless implementation of the browser would be called behind the scenes.
Alternatively, if you wanted to see the browser window when the tests ran, the headful implementation of Chrome would be used.
However, the awkward solution of having two separate browser implementations presented many maintenance headaches for both Google and test automation engineers.
Do you remember troubleshooting failed tests where the test would only fail in headless mode? That could have been due to the minor differences in the browser implementations. It used to be quite common for elements not to be found when running automated tests in headless mode. However, the same test would pass with flying colors if run in headful mode.
Chrome was upgraded in 2023 to eliminate many, if not all, pain points in the past solution.
Starting with Chrome 112, the headful and headless implementations of Chrome were unified. That means that the same browser implementation is in use whether your tests are run in headful or headless mode. The only difference is that Chrome will create, but not display, any platform windows in headless mode.
Among many of the benefits of the new headless Chrome upgrade is that tests that rely on having browser extensions installed will no longer be excluded in headless mode.
Headless mode now supports all browser-level functionalities.
How to do headless testing in Selenium
Selenium used to offer a
setHeadless() convenience method to set the browser execution mode. However, Selenium 4.8.0 deprecated using such a method, and Selenium 4.10.0 completely removed it.
If you are on Selenium 4.10.0 or later, use the
--headless=new flag instead. We have dedicated an entire article on how to run headless Selenium tests.
Headless mode benefits
Speed and efficiency
Headless testing eliminates the rendering of web pages, resulting in faster test execution. This efficiency is especially beneficial when running a large suite of tests, improving the overall testing process.
Without the need for a GUI, headless testing consumes fewer system resources like CPU and memory. Multiple tests can be run concurrently on the same machine without the strain of rendering web pages.
Headless testing allows for cost savings as it reduces the time and resources required to run tests. Fewer resources are needed, resulting in a more cost-effective testing process.
Integration with Continuous Integration (CI)
Headless testing integrates seamlessly with continuous integration tools, making it a crucial component of automated CI/CD pipelines. Tests can be run automatically upon code changes without requiring manual intervention.
Headless testing ensures compatibility across different browsers, enabling the execution of tests across multiple browsers in parallel without slowing down the process.
Headless mode limitations
Debugging can be more challenging in headless mode since there is no visual representation of the browser actions. Identifying and diagnosing issues can be time-consuming.
Limited real-world simulation
Headless mode may not accurately replicate user interactions in a real-world scenario. Certain user interactions, like mouse movements or hover effects, may not work as expected.
Final thoughts on headless testing in Selenium
Headless testing in Selenium has proven to be a game-changer in the web application testing field. Its efficiency, speed, and cost-effectiveness make it a popular choice for many developers and testers.
However, it’s essential to be aware of its limitations and choose an approach that aligns with the specific testing requirements of your project. By mastering headless testing and utilizing it effectively, you can enhance the quality and reliability of your web applications while optimizing the testing process.
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