The round count test is a good start, how about dropping it into sandy and between every mag. How about 10k rounds int 130 degree heat and 10k in sub zero temperatures?
Would like to see a machine slap the bolt release 100k times and see if there any wear around the pins and the pocket. Then make the machine slap the magzine release 100k times, and see if there's any wear. Then make it flick the safety 100k times and see if there's any wear.
I'd like to see a dummy, full weight solid upper and a solid magazine and a collapseable stock with a real buffer tube put on it and
watch it dropped onto concrete from 6 feet on the stock until it cracks.
watch it dropped onto concrete from 6 feet on the magazine until it cracks.
watch it dropped onto concrete from 6 feet on the barrel until it cracks.
watch it dropped onto concreet from 6 feet on either side until it cracks.
I'd like to see where it breaks, and how many drops it takes. If it doesn't break in 100 drops, call it a day.
Since you are producing it. I like for you to make sure a magazine locking deviced such as a Radlock (bullet button) will work on it (California strikes again). A flared magwell, and a provision for a tensioner screw to ensure a tightfit to any upper.
If you don't have a machine, I'd be more than happy to slap and flick a few dozen of them for you as a tester!
In all seriousness, if you can provide a hassle free lifetime warranty, that would put away any silence any doubters.