Angular, sinon stub not performing correctly

I am trying to mock a rootscope for a unit (karma/jasmine) test here, and it doesn't seem to be working. I'm not sure why and could use some help. Here it is :

Declaring it up top :

var mockRootScope = sinon.stub();

Inside the before each :

 angularMocks.module(function($provide) {
                    $provide.value('$rootScope', mockRootScope);
  });

Then inside the unit test itself

  mockRootScope.returns({
                    $id: 1
                });
                console.log(mockRootScope.$id);

the log is coming back undefined. if I log mockRootScope it tells me it's a stub (which is good), but I can't seem to figure out why it isn't returning correct values. Thanks!