[Jtsummers]

Matlab Simulink, probably. It's actually pretty neat, but I haven't touched it in over a decade now. It was useful for our embedded systems to have an executable model versus a prose specification document, and then it did get used to feed into the testing routine. Since the models were simpler to understand, confidence in them was higher. Differences in test results could be readily determined to be problems in the system and not the model after a quick analysis of the model ("Yep, that's supposed to be X, not Y" or "Nope, Y is correct, that's an error in the model here.").

[exdsq]

Simulink! That's the one! Thanks for the reminder - I googled but couldn't find it straight away.