Actually, it was FB that brought Newton up and mentioned him multiple times in the short post I was responding to. It was his attempt to correct me through the 'appeal to authority' logical fallacy. I never mentioned him before that. Afterwords, what you all were responding to was a direct quote from the man himself. So, all this talk about how it somehow undermines him or his work is actually quite interesting since the claim at its essence is that Newton undermines Newton.
As for a reasonable test, measurable curvature. There isn't any. There was a time a few years back, when free speech was still a thing in some quarters, when I could have pointed people to more tests than I could count where independent testers were measuring curve through multiple methods, and never finding one, but a lot of that has been scrubbed, buried in algorithm changes, or had their channels simply deleted. There are some remaining sources around I could point people to if they wanted to put some effort into actually learning about flat earth, but my estimate is well over 90% has been memory-holed.
A few years back, PBS did some Steven Hawking produced show where they 'measured' the curve, but that was great comedy. Every measurement they said they did had logical and/or editing flaws. People still bought it though, because confirmation-bias is still alive and kicking it seems.