Thursday, December 11, 2008

Selenium Field Notes

My last few projects have leveraged both Selenium-RC and Selenium-Core.  Here's a few notes from the field:

FireFox 3 doesn't work with Selenium 1.0.0 beta 1

When working with Selenium RC out of the box, Selenium stalls when trying to launch an instance of FireFox 3.  The Selenium-RC application works as a browser extension that is marked to only certain versions of the browser, this patch fixes the meta-data for the firefox plugin.

Instructions on how to fix the issue yourself can be found here, and within the comments there's a downloadable selenium-server.jar with the patch already applied.

Use Selenium-RC Judiciously

When you're working with Selenium Remote Control, every selenese command is sent over the network to the java application (even when working locally), so beware of redundant calls.  For example, I wrote several helper methods in my NUnit tests to group common selenese functions together:

public void SetText(string locator, string value) 

Since the "Click" event is only needed for a few commands, trimming down the selenese can improve execution speed:

public void SetText(string locator, string value) 
    SetText(locator, value, false) 
public void SetText(string locator, string value, bool clickBeforeType) 
    if (clickBeforeType) 

Avoid XPath when possible

Using XPath as a location strategy for your elements can be dangerous for long term maintenance for your tests as changes to the markup will undoubtedly break your tests.  Likewise, certain browsers (cough cough IE) have poor XPath engines and are considerably slower (IE is about 16x slower).

Strangely enough, following accessibility guidelines also makes for better functional UI testing.  So instead of XPath locators, consider:

  • Use "id" whenever feasible.
    <a id="close" href="#" onclick="javascript:foo();"><img src="close.gif"/></a> 
  • Use "alt" tags for images.
    <img src="close.gif" alt="close window" onclick="javascript:foo();" />
    selenium.Click("alt=close window");
  • Use text inside anchor tags when ids or images are not used.
  • <a href="/">Home</a> 

Avoid timing code

When working with AJAX or Postback events, page load speed can vary per machine or request.  Rather than putting timing code in your NUnit code (ie Thread.Sleep), take advantage of one of the selenium built-in WaitFor... selenese commands.

To use, you place javascript code in the condition where the last statement is treated as a return value.

// wait 30 seconds until an element is in the DOM
selenium.WaitForCondition("var element = document.getElementById('element'); element;", "3000");

This approach allows your code to be as fast as the browser rather than set to a fixed speed.

Use Experimental Browsers

When testing, I found several cases where I hit security limits, such as uploading a file.  In those cases, you have to use *chrome for Firefox and *iehta for Internet Explorer.  These browser profiles are just like *firefox and *iexplore, except that they run with elevated privileges.

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