of my friends smoked cigarettes in high school. He's probably been drunk a few times now too, not to mention I'd wager he's smoked/vaped pot. It's scary as a parent, no doubt, but I also think this is a pretty natural teenager phase, to include good successful college students who go on to do good things in life. Yes, nicotine is highly addictive and it's a vice that he will likely partake now and into college. That's the angle you need to keep hitting on IMO. The addictive qualities of tobacco and the recent news reports regarding vaping. Will it work? Probably not in the short term but it will set the groundwork to help ensure it's not an activity that extends into real world adulthood.

Of my 75% of friends that smoked in high school, I'd guess 10% of them smoke now. There may be some general correlation with success and the ones who don't still smoke cigarettes, use that too in speaking with your son.

Nicotine test is reasonable just to put the truth on the table to go from there...