**Warning:**This is probably totally unsupported, and might come with its own class of issues, but so far it seems to work...
To enable Mighty Moose in Visual Studio 2013 do the following steps:
Install Mighty Moose
Create a 2013 Addin file
C:\Program Files (x86)\ContinuousTests\AutoTest.VS.2012.Addinto
C:\Program Files (x86)\ContinuousTests\AutoTest.VS.2013.Addin
Edit the 2013 file and update the version numbers from
Or drop the following file:
AutoTest.VS.2013.Addinin your MightyMoose installation folder.
In Visual Studio open the Tools - Options - Environment - Add-in Security page and add
C:\Program Files (x86)\ContinuousTeststo the list of trusted add-in paths.
Restart Visual Studio
This seems to do the trick for me. Not sure if there are any issues with this, as I haven't played around with it too much. I had Visual Studio 2010, 2012 and 2013 installed side-by-side, so I didn't have to trick the installer into believing that there is a suitable version of Visual Studio anywhere.
See also: StackOverflow.