Comment by onalark

I don't think this would work for a number of reasons. If it's a database that you're modifying, you can see that a lot of operations (increment, delete, etc...) will do the wrong thing if they're called twice. If the operations themselves are idempotent, you wouldn't be able to verify that the intended side effect was correct. This is one reason developers spend a lot of time building mock objects: to capture "side effects".