N-N-N-N-N-NUnit!
I’m generally hesitant to pick up new tools that can be disruptive to my work style, but NUnit fits right in to my normal way of doing things. I write mostly middle tier stuff, so I start new tasks by creating a library project for my real code and a console application to unit test the library. Using NUnit was as simple as adding a reference to the NUnit.Framework assembly to my console project, adding the two NUnit attributes, and changing some of my Console.WriteLine statements to use the NUnit.Framework.Assertion class. Best of all, I can add the necessary stuff without losing the ability to run my unit tests as straight console apps at times when I don’t want to use NUnit.