stack/stack.go
func (s *Signature) SleepString() string {
	if s.SleepMax == 0 {
		return ""
	}
	if s.SleepMin != s.SleepMax {
		return fmt.Sprintf("%d~%d minutes", s.SleepMin, s.SleepMax)
	}
	return fmt.Sprintf("%d minutes", s.SleepMax)
}
func (s *Signature) SleepString() string {
	if s.SleepMax == 0 {
		return ""
	}
	if s.SleepMin != s.SleepMax {
		return fmt.Sprintf("%d~%d minutes", s.SleepMin, s.SleepMax)
	}
	return fmt.Sprintf("%d minutes", s.SleepMax)
}
// SleepString returns a string "N-M minutes" if the goroutine(s) slept for a
// long time.
//
// Returns an empty string otherwise.