We've been moving all of our unit tests from NUnit to Team System during the last couples of weeks and when we did I also wanted to improve the performance of some test so I was going to cache some data. I thought that using Isolated Storage (which is what we use in our production code) would be a good place, but it seemed like it did not work correctly. I started to debug the new cache code, and it never found the file. The reason was that the test project results in a new assembly each time it's compiled and because the assembly is part of the isolation in Isolated Storage there was no files in the store. This is of course obvious when you find it, but I guess easy to miss when writing tests.