code: func Clock() clock.Clock {
  	if tgt := os.Getenv("FAKECLOCK"); tgt != "" {
  		targetTime, err := time.Parse(time.UnixDate, tgt)
  		FailOnError(err, fmt.Sprintf("cmd.Clock: bad format for FAKECLOCK: %v\n", err))
  
  		cl := clock.NewFake()
  		cl.Set(targetTime)
  		blog.Get().Infof("Time was set to %v via FAKECLOCK", targetTime)
  		return cl
  	}
  	return clock.Default()
  }
docs: // Clock functions similarly to clock.Default(), but the returned value can be
  // changed using the FAKECLOCK environment variable if the 'integration' build
  // flag is set.
  //
  // The FAKECLOCK env var is in the time.UnixDate format, returned by `date -d`.