What version of VS do you have?
In the VS 2010 family, in my case Ultimate, for example, it is called Microsoft.VisualStudio.QualityTools.UnitTestFramework.dlland lives here C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PublicAssemblies\Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll.
If you have a version of VS 2008 or 2010 Express, you can still use http://www.nunit.org/ to test the modules.
, VS 2008 Architecture Edition Unit Test http://support.microsoft.com/kb/955869
Visual # 2010 Express?