The reality is there just isn’t many issues with new lenses other than copy variation. Modern lenses are pretty incredible. It’s almost always the photographer’s fault at this point.
It’s like they say a good carpenter never blames his tools.
Externally, there's not much to do beyond ensuring all the control surfaces and switches work as expected.
Internally, it's more important to do a good decentering test. Fred likes to do his diagonally, I prefer to do mine horizontally. I've saved myself some grief down the line by doing a quick 5 minutes test of every lens I buy.
