I would think it would depend on the quality of the company it’s coming from. For example, I could put a cheap bar in a rack, throw in some tow straps to each side right next to the collar and load the shit out of the straps without the bar permanently deforming. However, make Joe Sullivan squat 700 lbs with the same bar using non-calibrated plates and that same bar would catastrophically bend. Basically, factors like bouncing on a lifters back and how far out on the collar the weights are stacked can dramatically change how much load a bar can take before it permanently bends. Good companies will account for this, crap companies will do a static load test (bar never leaving the j-hooks) which will bias their bars towards better capacity.
Basically, there is no standard test. I know EliteFTS has done dump tests with some of their bars, where they actually load a bar, have a lifter walk it out, and then dump it off their back down to the safeties, but at the end of the day “you get what you pay for” kind of holds true.