Is there any way to setup RhinoMocks expectation without caring about return value? Something like that:
repository.Expect(r => r.Add(1)).Return(Anything)
Note that if you don't specify a return value the default will be returned. So null for objects, false for bool, 0 for int, etc.
So in your case, if you are expecting one call to the method, you could write
repository.Expect(r => r.Add(1)).Repeat.Once();