func FuzzyDuration(d, fuzz time.Duration) time.Duration {
	if fuzz < 0 {
		return d
	}
	// apply range [-fuzz/2, fuzz/2]
	d += time.Duration(rand.Int63n(int64(fuzz)+1) - (int64(fuzz) / 2))
	if d < 0 {
		return 0
	}
	return d
}