When trying to setup unit testing I was slightly dissapoited you couldn't test a silverlight library using a normal test project. However you can use the testing framework by using the Silverlight 3 libraries here.
However you have to make sure you get the right version. I didn't and instead I found a link to an older tutorial and got the nice error
Cannot find a Resource with the Name/Key typeNameConverter and the only real match for the error had a broken link. The solution was simple though, find the source and update to the Mango version.