When setting up a Silverlight Unit Testing class the following using statements and inheritance must be applied:
These are required for the TestPanel and EnqueueX methods (particularly inheritance).
For more on the Inner Class Pattern, take a look at the Type Mock training blog.
Mark Cooper 
Typemock have released Silverunit, an open source Typemock add-on for unit testing Silverlight. It may help with writing your tests. http://www.typemock.com/Silverlight_unit_testing_page.php
Thanks, I’ll take a look.