Related Clues:

• Challenged
• Quizzed
• Tried out
• Put under pressure
• Assayed
• Proven in trials
• Put through a trial
• Tried-and-true
• In repose
• Took for a trial run
• Challenged, or what the theme entries in this puzzle should be
• Took out for a spin
• Stuck a toe in
• Worked on in the lab
• Pushed to the limit