> We don't have any behavior specified in this case, and as I mentioned before, I didn't even know this was a thing.

It's not defined in a scenario, but that doesn't mean that the behavior doesn't exist. What happens when you try to charge a card $100mm?

> Then.... they'll have a bug? I'm sorry, I must be seriously misunderstanding what your point is.

What's supposed to catch that bug other than the scenarios?