Where is mstest.exe located?

I need to run mstest from the command line - where in the world is this exe located? Can anyone give me a clue?

Edit: I only have Visual Studio 2010 installed

for %x in (mstest.exe) do @echo.%~dp$PATH:x

from the Visual Studio Command Prompt is your friend. For me it's in

C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\