I get asked about automated testing of WPF apps quite often.  WPF has a nice feature called UI Automation.  From the UI Automation Overview page on MSDN:

"Microsoft UI Automation is the new accessibility framework for Microsoft Windows, available on all operating systems that support Windows Presentation Foundation (WPF).

UI Automation provides programmatic access to most user interface (UI) elements on the desktop, enabling assistive technology products such as screen readers to provide information about the UI to end users and to manipulate the UI by means other than standard input. UI Automation also allows automated test scripts to interact with the UI."

UI Automation is what you would use to do automated testing of your WPF apps.  There are a set of helpful links to get you started here.

-Marc