So when testing a Portable Class Library without any platform specific code, is testing against just one of the platforms (.net 4.5) from the profile enough? My intuition says no, but I've read some claims otherwise.
And if you do need to test against each platform, do any of the multitude of test frameworks out there for .net have a PCL testing library with runners for each or most platforms, so only one DLL of unit tests would be necessary?
It's usually best to test on all platforms. Right now I'm not aware of any test framework/runner that supports this. I'm hoping to help xUnit do so.
I've done a very simple implementation of a test framework for my PCL Storage library. So you could use that to get you started running tests on all the platforms.