I looked into that mouth swap test as soon as I heard about it a couple of years ago (while it was still in development), there's 3 company's make them but they're all similar.
It's like a swabbed pregnancy test for weed residue, very very basic tech.
Different tests for different stuff. Coke is one test, cannabinoids another.
I'm not sure exactly how the Coke test works because it doesn't really concern me but I spent serious time researching the Cannabis test.
It can't detect systemic THC like a urine test can, it only detects residues left in your mouth up to a certain amount of time after smoking (along the lines of 3-5 hours I think) and even then it's efficacy is patchy at best (30% ish).
All they know then is that you have consumed within a certain time frame of driving, that's it.
Proving impairment to drive is a different matter, there's no framework set up for prosecution to partner them, these test kits are pitched privately to the cops by the firms that make them, I think the main one started off as a kickstarter project ffs.
Alcohol fucks it right up though cos it washes away the trace amounts of non water soluble THC stuck to the inside of your mouth.
High alcohol content mouthwash is your answer, Listerine is the strongest at about 97-98% ethanol.
A good swill of strong mouthwash before you leave the house to drive and there should be nothing to worry about.
You may fail a road side alcohol breath test on the flip side to that though.