Selenium WebDriver tips 2

1. "Xpath expression cannot be evaluated or does notresult in a WebElement" error

During our recent automation project we've been encountering really irritating error using WebDriver

"The xpath expression '//given xpath' cannot be evaluated or does notresult in a WebElement"

This error was appearing randomly, for example script was working for 10 times but failed on the 11th. Eventually after several experiments we were able to narrow the problem to following factors:

- this problem appears on the IE only(IE8 in our case)
- this problems appears when WebElement is identified using XPath selector
- this problems appears often shortly after webpage is loaded

Possible Solutions:

Get rid of the XPath selectors
This is great idea and Alister Scott presents sound arguments for this here. This approach however is not always applicable in our context. We know that sophisticated XPath selectors can be brittle but having to automate application based on Microsott SharePoint there is not much choice

Add pause before first FindElement (with XPath selector) method
This solution worked out however you need to remember about adding this pause every time new page is opened. Because in general we don't like pauses in our automation scripts for many reasons we were looking for something else.

Update current FindElement method
We found this solution indirectly thanks to Alister Scott and his SpecDriver example on github. Because this problem appears usually at the first attempt to find element using XPath it's easy to update FindElement method and create your own where you can catch the exception for given number of times. An example in C#:

for (int i = 1; i <= 10; i++)
{
try
{
return driver.FindElement(selector);
}
catch (OpenQA.Selenium.WebDriverException e)
{
Console.WriteLine("Error " + i + " raised: " + e.Message);
}

It really works and often above loop doesn't need more than two iteration to return correct WebElement.

2. WebDriver loses focus on IE8

Another issue which appears randomly. Fortunately we were able to identify one of the reason of this issue - Microsoft Office Communicator. In order to run tests using WebDriver on IE (Windows 7, IE8 in our case) Microsoft's IM needs to be switched off if not then WebDriver randomly switches from IE to IM window during script execution.

Alek