Check out this whitepaper – How to Configure a Stress Test Project for Microsoft Office SharePoint Server 2007 using Visual Studio Team Suite 2008.
I have experienced some availabilty problems with the link, and because of that, You will also be able to get a local copy of the whitepaper from here:
HowToConfigStressTestProjectForMOSS07usingVS2008TS
If you want more information on VS and testing, You should check out the blog of Ed Glas