I don't remember anyone here ever saying that proof testing is the ultimate end all for determining firearms safety but it is still used today extensively yes extensively in the US and the by the US military as well. It is not a useless outdated testing method when done properly.
I am going to state that nothing should fail proof testing. If a firearm fails proof testing then the entire production facility should be shut down, all processes examined, all materials in process tested and re certified, and all workers re trained. And a lot of management officials should be let go.
Production technology has improved considerably in my lifetime. I toured the GM Arlington plant in 1982. There was inventory all over the place, the place looked like a junk yard. At the end of the assembly line, just as the group walked up, seven guys were pushing a car off the the side because it would not start. That car went into a row of vehicles that were being debugged. I remember a quote from a GM executive from the 1970's, he said "Production builds it, marketing sells it, and customer service makes it work". That was the attitude of the time and it is no wonder that GM almost went bankrupt. (in the 1980's while Toyota's were selling above MSRP, GM was selling Nova's, which were rebranded Toyota Corolla's, for a discount) I have toured the Mercedes plant (1990's) and the Corvette plant (2017), and at the end of the production line asked the tour guide,
"how many vehicles have not started up?". That actually startles the tour guides, typically they were born decades after my first plant tour, and none that I have asked could remember a vehicle not starting up and driving away.
Design verification tests are only conducted once for the vast number of military equipment. There is no reason, and the cost is prohibitive, to stress each and every item to its design limits. I consider a proof test a DVT type test, and in my opinion, un necessary in a ISO 9000 world. But if it makes the consumer feel better, because the consumer simply does things because Grandpa did it that way, well, manufacturer's will respond to keep the consumer from going irrational happy to irrational unhappy. However, I will say, based on the incalculable number of hot loads shooters report using on the internet, irrationality is alive, well and thriving. The typical attitude is,
"if my gun has not blown up (yet) then it must be safe!" Just read any surplus ammunition thread I have commented in, I have shown lots of blown up firearms with old ammunition, but the majority consensus of the shooting community is, "
it's cheap therefore it has to be good".
I invite all those who think there is a Federally Mandated US proof test, to search the
Code of Federal Regulations and find the section. If is not there, then it does not exist. In the US, proof testing is anything the manufacturer wants it to be. Or in case of the Army, whatever the Army is willing to pay, and the contractor is willing to accept.
If the OP creates his own, uninstrumented proof test, and stresses the materials close to, or above its design limits, he has simply shortened the number of cycles it will take for the cylinder to rupture. If there is any real concern about the workmanship of the piece in question, it is far better not to shoot the thing. The consequences of a severe accident, such as losing an eye, losing a hand, or a frame in the brain, are not only irrecoverable, they are not worth the price of a cheap firearm.