> At the time I was also told the most popular "test" SKU used by Amazon engineers was a 50 gallon barrel of lube.
Not knowing when this was, but I can say around 2013-2015 that this wasn't a general thing[0]. Could there have been an engineer who used it a lot? Sure, but there's a lot of them.
Even if you disregard the crudity of it, it also just doesn't make for a good test ASIN outside of a small number of verticals. You'd much rather test with real ASINs where possible (which is almost 100% of the time), or with something idiomatic to the experience you're developing.
EDIT: though maybe people have become inspired by https://observer.com/2015/07/at-1k-55-gallon-bottle-of-lube-... ? Still, it stands to reason that you want to test with real products whenever you can.