Nissan's method of testing engine durability is to rev the engine constantly at full revs, for 24 hours! Fiat probably have a similar method being Italian!
Nearly all engines will have been tested to destruction at some point by the manufacture.
Ford done one of their engines, started it from cold, throttle wide open, and just left it, without full cooling capacity, and it ran at full throttle for three and a half weeks before going bang. Now that is one durable engine! (can't remember which one it was though ).