tester

/ˈtɛstər/
noun
  1. A person or thing that tests something, such as a product, system, or idea.
    • Before launching the game, the company hired a team of testers to play it.
    • The software tester found several bugs in the new app.
    • The car's safety features were evaluated by a professional tester.
  2. A small sample of a product, especially a cosmetic or perfume, used to try before buying.
    • She sprayed the tester of the new perfume on her wrist.
    • The store had testers for all the lipstick shades so customers could try them.
    • I always use the tester before buying a new foundation.
  3. A device or tool used to measure or check something, such as electrical current or battery power.
    • A circuit tester can help you find a broken wire.
    • He used a battery tester to see if the remote needed new batteries.
    • The electrician checked the outlet with a voltage tester.