When someone is a tester, they either administer tests or they assess the safety or function of a product. You might hope for an eventual career as a bubblegum tester.
When you take a standardized exam, a tester will hand out papers and collect them when your time is up. And when you get a driver's license, a tester will ride along with you in the car during your road test. There's another type of tester that's a free sample, like a lipstick tester you can try on in a store. And an old-fashioned tester is the fabric canopy on the top of a four-poster bed.