Headless Browser & Testing


What is Headless Browser?

Headless Browser is a browser without a Graphical User Interface.

Unlike a normal browser, Headless Browser doesn’t show webpages to the user and can pipe the contents to another program. When you start a Headless Browser, you won’t be able to see the content on the screen because everything is running in the background.

Like a normal Browser, the headless browser is capable of parsing and interpreting web pages. In short, we can say the headless browser is capable of providing all the capabilities of a normal browser without taking a toll on system memory and speed. For example, the headless browser can cope without all sorts of downloads, parsing JavaScript and many more functionalities

Usefulness and problem overcoming’s of Headless Browser Testing

In the end, the only tests that matter are end-to-end UI-driven tests. These are the tests that begin and end with the application’s interfaces and prove that the application—with all of its events, queues and microservices—allows the stakeholders to meet all of their goals.

But there are some inherent problems with UI-driven testing. Stability is one: Even when the application is working correctly, UI-driven tests occasionally fail when interacting with the browser. Performance is the other issue: UI-driven testing is sloooooooowwww compared to other kinds of automated testing.

“Headless browser testing improves both the effectiveness and efficiency of your testing process while integrating quality assurance with software delivery.”

Examples Of Headless Browsers

There are various Headless Browsers available.

Enlisted below are some examples:

  • Html Unit Browsers
  • Firefox
  • Chrome
  • PhantomJS
  • Zombie.js
  • TrifleJS
  • SlimerJS
  • Splash
  • SimpleBrowser
  • NodeJS

Headless HtmlUnitDriver

What Is HtmlUnitDriver?

HtmlUnitDriver is a Headless web browser written in Java. The name suggests it is a Headless driver which is based on HTML Unit. HtmlUnitDriver is a built-in headless browser in Selenium WebDriver. It is considered to be the most lightweight and fast browsers.

Let’s move on to the implementation of the HtmlUnitDriver. The HtmlUnitDriver JAR files can be downloaded from the official website of Selenium.

HtmlUnitDriver In Headless Mode

Just like all the other browsers, for the HtmlUnitDriver as well, we need to create an object for the class to run the code in headless mode.

Thus on executing the code for HtmlUnitDriver in Headless mode, the Output received displays the Title of Page and its URL. The Output is received through the Console where all the functions performed in the program can be viewed in a stepwise manner.

Given below is the screenshot of the executed code:

HtmlUnitDriver In Headless mode

Features/Advantages Of HtmlUnitDriver

Features of HtmlUnitDriver

  • Provides support for HTTPS and HTTP protocols.
  • Great support for JavaScript.
  • Helps in Multitasking, thereby allowing to run multiple tests.
  • Provides support for Cookies. Also, supports Proxy Servers.
  • Improves the performance and speed of test scripts, as it has the fastest implementation of WebDriver.
  • HtmlUnitDriver is platform-independent.
  • As it is Headless by default, it supports Headless Testing.

Disadvantages Of HtmlUnitDriver

  • The use of HtmlUnitDriver is not possible for complex websites.
  • While comparing with a real browser testing, for headless browsers like HtmlUnitDriver, it becomes very difficult for debugging the script.
  • The generation of screenshots is not possible with HtmlUnitDriver.
  • Headless Browsers emulate other browsers.


Thus, we can say Headless browser is a very good technique when you require fast feedback, want to test snippets of code fast and without a hassle to start a browser and also, they are quick to set up. But with all the advantages, like a coin, it also has 2 sides. The headless browser can be limiting if you want to do full GUI Testing or for the matter if you want to test all the varieties of the browser OS combination to ensure full test case coverage. For instance, debugging tools like video validation cannot be accessed in headless mode.

With this, we are done with Headless Browser Testing, a strategy that has both pros and cons. It is up to you to decide how to utilize it to its fullest power.


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