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