VS 2008
From Richard's Wiki
When creating a "Test" project in Visual Studio, the following element
is added to the csproj xml in the very first PropertyGroup element:
<ProjectTypeGuids>{3AC096D0-A1C2-E12C-1390-A8335801FDAB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
If you created your test assembly by hand, say by creating a new Class Library
and adding a reference to Microsoft.VisualStudio.QualityTools.UnitTestFramework,
this element will not be in your csproj file and visual studio will ignore all
the tests located inside. Add the element and all will be good again.
Snippets
Add this code to My Documents\Visual Studio 2008\Code Snippets\Visual C#\My Code Snippets