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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
package maths
import (
"slices"
"testing"
"time"
)
// some real world latency samples.
var (
latencyHistory1 = []int{
14, 12, 15, 6, 19, 12, 13, 13, 13, 16, 17, 11, 17, 11, 14, 15, 14, 15,
16, 16, 17, 14, 12, 16, 18, 14, 14, 11, 15, 15, 25, 11, 15, 14, 12, 15,
13, 12, 13, 15, 11, 13, 15, 14, 14, 15, 12, 15, 18, 12, 15, 22, 12, 13,
10, 14, 16, 15, 16, 11, 14, 17, 18, 20, 16, 11, 16, 14, 5, 15, 17, 12,
15, 11, 15, 20, 12, 17, 12, 17, 15, 12, 12, 11, 14, 15, 11, 20, 14, 13,
11, 12, 13, 13, 11, 13, 11, 15, 13, 13, 14, 12, 11, 12, 12, 14, 11, 13,
12, 12, 12, 19, 14, 13, 13, 14, 11, 12, 10, 11, 15, 12, 14, 11, 11, 14,
14, 12, 12, 11, 14, 12, 11, 12, 14, 11, 12, 15, 12, 14, 12, 12, 21, 16,
21, 12, 16, 9, 11, 16, 14, 13, 14, 12, 13, 16,
}
latencyHistory2 = []int{
18, 20, 21, 21, 20, 23, 18, 18, 20, 21, 20, 19, 22, 18, 20, 20, 19, 21,
21, 22, 22, 19, 18, 22, 22, 19, 20, 17, 16, 11, 25, 16, 18, 21, 17, 22,
19, 18, 22, 21, 20, 18, 22, 17, 17, 20, 19, 10, 19, 16, 19, 25, 17, 18,
15, 20, 21, 20, 23, 22, 22, 22, 19, 22, 22, 17, 22, 20, 20, 19, 21, 22,
20, 19, 17, 22, 16, 16, 20, 22, 17, 19, 21, 16, 20, 22, 19, 21, 20, 19,
13, 14, 23, 19, 16, 10, 19, 15, 15, 17, 16, 18, 14, 16, 18, 22, 20, 18,
18, 21, 15, 19, 18, 19, 18, 20, 17, 19, 21, 19, 20, 19, 20, 20, 17, 14,
17, 17, 18, 21, 20, 18, 18, 17, 16, 17, 17, 20, 22, 19, 20, 21, 21, 20,
21, 24, 20, 18, 12, 17, 18, 17, 19, 19, 19,
}
)
func TestEWMALatencyHistory(t *testing.T) {
type result struct {
t time.Time
v float64
s int
}
for _, latencyHistory := range [][]int{latencyHistory1, latencyHistory2} {
startTime := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
halfLife := 30.0
ewma := NewEWMA(halfLife)
var results []result
sum := 0.0
for i, latency := range latencyHistory {
t := startTime.Add(time.Duration(i) * time.Second)
ewma.Update(float64(latency), t)
sum += float64(latency)
results = append(results, result{t, ewma.Get(), latency})
}
mean := sum / float64(len(latencyHistory))
min := float64(slices.Min(latencyHistory))
max := float64(slices.Max(latencyHistory))
t.Logf("EWMA Latency History (half-life: %.1f seconds):", halfLife)
t.Logf("Mean latency: %.2f ms", mean)
t.Logf("Range: [%.1f, %.1f]", min, max)
t.Log("Samples: ")
sparkline := []rune("▁▂▃▄▅▆▇█")
var sampleLine []rune
for _, r := range results {
idx := int(((float64(r.s) - min) / (max - min)) * float64(len(sparkline)-1))
if idx >= len(sparkline) {
idx = len(sparkline) - 1
}
sampleLine = append(sampleLine, sparkline[idx])
}
t.Log(string(sampleLine))
t.Log("EWMA: ")
var ewmaLine []rune
for _, r := range results {
idx := int(((r.v - min) / (max - min)) * float64(len(sparkline)-1))
if idx >= len(sparkline) {
idx = len(sparkline) - 1
}
ewmaLine = append(ewmaLine, sparkline[idx])
}
t.Log(string(ewmaLine))
t.Log("")
t.Logf("Time | Sample | Value | Value - Sample")
t.Logf("")
for _, result := range results {
t.Logf("%10s | % 6d | % 5.2f | % 5.2f", result.t.Format("15:04:05"), result.s, result.v, result.v-float64(result.s))
}
// check that all results are greater than the min, and less than the max of the input,
// and they're all close to the mean.
for _, result := range results {
if result.v < float64(min) || result.v > float64(max) {
t.Errorf("result %f out of range [%f, %f]", result.v, min, max)
}
if result.v < mean*0.9 || result.v > mean*1.1 {
t.Errorf("result %f not close to mean %f", result.v, mean)
}
}
}
}
func TestHalfLife(t *testing.T) {
start := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
ewma := NewEWMA(30.0)
ewma.Update(10, start)
ewma.Update(0, start.Add(30*time.Second))
if ewma.Get() != 5 {
t.Errorf("expected 5, got %f", ewma.Get())
}
ewma.Update(10, start.Add(60*time.Second))
if ewma.Get() != 7.5 {
t.Errorf("expected 7.5, got %f", ewma.Get())
}
ewma.Update(10, start.Add(90*time.Second))
if ewma.Get() != 8.75 {
t.Errorf("expected 8.75, got %f", ewma.Get())
}
}
func TestZeroValue(t *testing.T) {
start := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
var ewma EWMA
ewma.Update(10, start)
ewma.Update(0, start.Add(time.Second))
if ewma.Get() != 5 {
t.Errorf("expected 5, got %f", ewma.Get())
}
ewma.Update(10, start.Add(2*time.Second))
if ewma.Get() != 7.5 {
t.Errorf("expected 7.5, got %f", ewma.Get())
}
ewma.Update(10, start.Add(3*time.Second))
if ewma.Get() != 8.75 {
t.Errorf("expected 8.75, got %f", ewma.Get())
}
}
func TestReset(t *testing.T) {
start := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
ewma := NewEWMA(30.0)
ewma.Update(10, start)
ewma.Update(0, start.Add(30*time.Second))
if ewma.Get() != 5 {
t.Errorf("expected 5, got %f", ewma.Get())
}
ewma.Reset()
if ewma.Get() != 0 {
t.Errorf("expected 0, got %f", ewma.Get())
}
ewma.Update(10, start.Add(90*time.Second))
if ewma.Get() != 10 {
t.Errorf("expected 10, got %f", ewma.Get())
}
}
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