So you have some conditional logic in your production code, such as a switch on this enum value, and you want to test the default clause if you don't recognise any of the options?
For example:
In this scenario are you wanting to mock the Option enum so that you can force it to drop through to the default?
If so you might want to have a read through
this thread. We had a similar discussion on this topic a short while back.
If this is not the scenario you are facing then please elaborate further.