Сценарий 1:
var myInterface = MockRepository.GenerateStub<IMyINterface>();
myInterface.Stub(x => x.GetMeSomeIngeter()).Return(5);
Сценарий 2:
var myInterface = MockRepository.GenerateStub<IMyINterface>();
myInterface.Stub(x => x.GetMeAToy("Gizmo")).Return(new Toy() {ToyName = "Gizmo", Code = "0989"});