http://msdn.microsoft.com/asp.net/?pull=/library/en-us/dnaspp/html/aspnet-testwithnunit.asp
This is my latest MSDN article, an introduction to NUnit as well as some lessons learned for unit testing a data access layer. I don’t claim to be a unit testing expert, but these techniques have definitely helped me when I have had the discipline to apply them. Hopefully it will help a few folks to avoid some of the problems I encountered along the way.