Comparative analysis of the WebDrivers’ Drivers

While working with selenium webdriver you have an option to choose from multiple webdrivers, such as HtmlUnitDriver, FirefoxDriver, InternetExplorerDriver, ChromeDriver and OperaDriver. Each one of them is a separate implementation of the WebDriver interface provided by Selenium. All of them have unique advantages and disadvantages because of the implementation differences for catering to different requirements. It is good to know the comparative advantages and disadvantages of each one before picking one of them.

The first major point to note is that there are two groups of driver implementations. One of those that invoke the actual browser installed on your system and the other that emulates the behavior of another browser. FirefoxDriver, InternetExplorerDriver, ChromeDriver and OperaDriver invoke the actual browser installed on the machine; however the HtmlUnitDriver emulates other browsers JS behavior. 

HtmlUnitDriver

 HtmlUnit is a java based framework for testing webApps basically a wrapper around ‘HttpClient’ by Jakarta. HtmlUnit provides UI-Less emulation of browsers to test web applications. The HtmlUnit APIs let you do the typical functions performed in an actual web browser, such as click links, fill forms, invoke web pages, submit values etc. HtmlUnit supports java script and complex AJAX libraries. Javascript is disabled in the HtmlUnitDriver by default, however if it can be enabled if required. The mechanism to enable javascript with the HtmlUnitDriver is as follows:

HtmlUnitDriver MyhtmlDriver = new HtmlUnitDriver();

 MyhtmlDriver.setJavascriptEnabled(true);

OR

HtmlUnitDriver MyhtmlDriver = new HtmlUnitDriver(true);

When enabled, the HtmlUnitDriver emulates the java script behavior of Internet Explorer by default. However we can direct the HtmlUnitDriver to emulate the JavaScript behavior of the browser of our choice by invoking the constructor that accepts the browser version. This can be done as follows:

HtmlUnitDriver MyhtmlDriver = new HtmlUnitDriver(BrowserVersion.Firefox_2);

Internet Explorer Driver

 The IE driver class ‘InternetExplorerDriver.class’ is located at ‘\org\openqa\selenium\ie\’ directory in the ‘selenium-server-standalone-2.7.0.jar’. To use the InternetExplorerDriver all you need to do is to have the selenium-server-standalone-2.7.0.jar in your CLASSPATH.  The IE driver runs only on windows and supports both 32-bit and 64-bit operations. Depending on the thread that instantiates the InternetExplorerDriver corresponding version of the IE is launched i.e. if the thread instantiating driver is running in 32-bit then the 32-bit version of the IE will be launched and if the thread instantiating driver is running in 64-bit then the 64-bit version of the IE will be launched.

The Internet Explorer driver uses the native or OS-level events to perform various functions on the browser, such as inputs from keyboard and mouse. This approach has both advantages and limitations both. The advantages are that it bypasses the limitations of the Javascript sandbox but there can be issues like the browser window under test might be out of focus.

Firefox Driver

‘selenium-server-standalone-X.X.X.jar’ contains all the drivers implementing the WebDriver interface of selenium. Hence the 'FirefoxDriver.class' can be found in the ‘\org\openqa\selenium\firefox directory in the selenium-server-standalone-X.X.X.jar. The driver when instantiated is added as an extension to the firefox profile. You can specify the profile with which you want to load firefox session. If no profile is specified then the driver creates an anonymous profile by default.
A profile can be created for the firefox driver as follows:

FirefoxProfile myProfile = new FirefoxProfile();

Multiple operations can be performed on the newly created profile, such as:

myProfile.addExtension(File);
myProfile.clean();
myProfile.getPort();
myProfile.setPort(int port);
myProfile.enableNativeEvents();
myProfile.setPreference(String key, String value); etc...

After creating the your profile you can pass the profile while creating the driver instance as follows:
WebDriver myFireFoxDriver = new FirefoxDriver(myProfile);

This driver is faster than the InternetExplorerDriver and executes the test in real Firefox web browser.