I thought it would be nice to see and have access to a bit more information when the transition is invalid. This changes theRuntimeError to a customStatefulEnum::InvalidTransition exception. The error message contains the state and the event that was attempted. Those 2 pieces of information are also stored on the exception itself for easy access.

I almost took it a step further by adding what the state would have been if the event had succeeded – e.g. in the test below:Invalid transition from "resolved" to "assigned" via event :assign!' – but that would take significantly more work. I believe the solution to that would require storing the events in memory. I'm not even sure how useful it would be to know that information. But if you like the idea, I would be happy to continue to explore the idea.