What is XPath 

XPath is a small language that describes the pathc to parts of a web page.  Selenium can use it to click on things, change fields, or assert against values of fields.

XPath trial and error

Brian Slesinsky has a great tool called XPath Checker for Firefox.  Its a plugin, that is well worth installing into Firefox.

There is another, more well known plugin called Firebug for Firefox. It allows you to inspect a page at run time.  With the advent of AJAX web apps, there where a page structure is only apparent at run time, then it is invaluable. Read more about Firebug at its site.

It would be great if the features of XPath checker were rolled into Firebug!  But for now, they are not so install them both into Firefox if you evolving a test suite.

Using the 'email' example of the GWT sample applications, to illustrate the point, we have loaded it up and gone into firebug (below).  Clicking 'Inspect'' (1) in Firebug's toolbar and clicking on a node in the page (2) takes you to the relevant html that represents it (3).  There are some breadcrumbs that show where you are in the page (4)......



If you right-click on that breadcrumbs place, you can get to a menu that will give you xpath for it...




Using that menu, gives the following as the xpath for that node ...

    /html/body/table/tbody/tr[2]/td[2]/table/tbody/tr/td/table/tbody/tr[5]/td[2]

Bug that is too unweildy for use in a Selenium script.  Use XPath Checker to make it more concise. Shown here with the original long (and ugly) Xpath locator for that node, finding exactly one matching node:


After looking again at the node in Firebug, we can modify the XPath to the following, and get closer, but have too many results:


 
Here we try again, knowing that its array element 2 that were are interested in:



That.s much better, but we may want to survive colum reordering.  Perhaps we knew the email address we were looking for in the first place:


Or maybe we knew that it was an email address in that field, and could leverage the fact that all emails contain @ characters:


So XPath checker allows us to play with Xpath expressions making them more terse and resiliant to change.  You can cut/paste them out of XPath Checker and into your test scripts.

Our advice is to use ID attrubutes where you can though:


This works great, except when the application you're testing has no ID attributes.