I have created a Mono for Android VS2010 project and added NUnit tests.
It seems Mono for Android does not support NUnit according to this post from Xamarin: https:/
I created a version of NUnitLite that targets MonoDroid. It's worked quite well for me so far.
It needs to run directly on the emulator or device at the moment. If someone were able and inclined to write a runner for it, I'd welcome the input.
Check it out here: https://github.com/SpiritMachine/NUnitLite.MonoDroid