Here's a great article on testing environments in .Net, co written by Andrew Stopford (and Jay Flowers) -  Unit Testing with VSTS, NUnit and MbUnit . I must admit I usually just make my own test systems, maybe due to always needing to cross back and forth between swf gen code and .Net. However reading this I see I'm really needing to give MbUnit a look. Here is an example one thing that seems super cool:

 [RowTest()]
[Row(1,2,3)]
[Row(2,3,5)]
[Row(3,4,8)]
[Row(4,5,9)]
public void tAdd(Int32 x, Int32 y, Int32 expectedSum)
{
  Int32 Sum;
  Sum = this.Subject.Add(x,y);
  Assert.AreEqual(expectedSum, Sum);
}

Notice how you can pass different sets of args on the attributes - very neat : ). Setting time aside this weekend for a closer look...