I just cloned the gruntjs repository.
How do I actually run the tests for GruntJS?
(I don't mean I want to run my own tests using GruntJS. I mean that I want to run the tests for GruntJS itself.)
grunt test
should do the trick.
Grunt eats its own dog food.
git clone https://github.com/gruntjs/grunt
cd grunt
grunt test
Or, like any grunt repository (because the package.json is well-formed):
cd grunt
npm test