Here’s a couple of useful links on testing for Windows Phone applications:
Unit testing for Windows Phone apps
Options for publishing Windows Phone beta apps and testing in-app purchase
One additional comment I would make about unit testing for Windows Phone is that unfortunately the tests written using a Visual Studio Windows Phone unit testing project can’t be executed (easily) as part of a Visual Studio Online automated build. The work around for this is to place most of your business logic in a Portable Class Library and to simply use a regular unit testing project to test the functionality. Of course, this isn’t as accurate as testing using either the emulator or a real device but it will give you some level of regression testing with each build (ideally after each check in).
