The mint test is administered
immediately before trying to take a girl home. If
you're not sure if a gal wants to get down, ask her if she'd like a mint. If she's into you she'll want to make sure her breath is fresh before anything happens. If she passes the mint test ask her back to your place. If not, get her number and good luck.
This all assumes that both parties haven't already started
making out at the bar with nasty cigarette and booze breath.