Visual Studio 2012 Update 2 has changed something in MSTest so that it broke compatibility with ReSharper. From the description it seems it forced JetBrains to release next version on ReSharper, so users of R# had problems only for one week. Great work, actually: I bet it is not a trivial task to establish development process that allow something of R# caliber to be released in one week.
Though it is another nail to MSTest coffin, IMO. It is not only stuck in place and not evolving (gosh, they can’t make asserts for exceptions or even fix bug that ExpectedException attribute don’t check message even if asked to for years!), but actually disrupt work process from time to time with breaking changes, strange SEH exceptions or incompatibilities.
I’m extremely happy we were able to abandon MSTest and adopt NUnit.
If you have new project and deciding which unit-test framework to use – do yourself a favor and avoid MSTest as much as possible.