code: func (cc *Controller) checkTrial(duration time.Duration) {
  	// when the trial period is over, the assigned config becomes the last-known-good
  	if trial, err := cc.inTrial(duration); err != nil {
  		utillog.Errorf("failed to check trial period for assigned config, error: %v", err)
  	} else if !trial {
  		if err := cc.graduateAssignedToLastKnownGood(); err != nil {
  			utillog.Errorf("failed to set last-known-good to assigned config, error: %v", err)
  		}
  	}
  }
docs: // checkTrial checks whether the trial duration has passed, and updates the last-known-good config if necessary