public void WhenArgumentIsAnything() { IModelRepository mock = MockRepository.GenerateMock <IModelRepository> (); var modelCreator = new ModelCreator(mock); var theModel = new AnotherModel() { FieldA = 1, FieldB = "Test" }; mock.Expect(p => p.Add(Arg <AnotherModel> .Is.Anything)); modelCreator.CreateModel(theModel); mock.VerifyAllExpectations(); }