Mechanical things allow a surprising amount of modularity, compared to software, and therefore make it easy to get test coverage.
E.g. your cable is rated for 10,000 kg and 6-month inspections, your driveshaft can go 5 million revolutions or 9 months before it needs to be greased...test all those things separately, put them together and you have a stateless system that if it works today will work tomorrow.
E.g. your cable is rated for 10,000 kg and 6-month inspections, your driveshaft can go 5 million revolutions or 9 months before it needs to be greased...test all those things separately, put them together and you have a stateless system that if it works today will work tomorrow.