package main

import (
    "fmt"
    "math/rand"
    "testing"
    "time"
)

func TestFoo(te *testing.T) {
    start := time.Now()
    var t *time.Timer
    t = time.AfterFunc(randomDuration(), func() {
        fmt.Println(time.Now().Sub(start))
        t.Reset(randomDuration())
    })
    time.Sleep(5 * time.Second)
}

func randomDuration() time.Duration {
    return time.Duration(rand.Int63n(1e9))
}

$ go test -race racy_test.go
948.011474ms
==================
WARNING: DATA RACE
Read by goroutine 8:
  command-line-arguments.TestFoo.func1()
      /home/alberto/Desktop/racy_test.go:15 +0x1b4

Previous write by goroutine 6:
  command-line-arguments.TestFoo()
      /home/alberto/Desktop/racy_test.go:16 +0x14d
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:456 +0xdc

Goroutine 8 (running) created at:
  time.goFunc()
      /tmp/workdir/go/src/time/sleep.go:129 +0x6d

Goroutine 6 (running) created at:
  testing.RunTests()
      /tmp/workdir/go/src/testing/testing.go:561 +0xaa3
  testing.(*M).Run()
      /tmp/workdir/go/src/testing/testing.go:494 +0xe4
  main.main()
      command-line-arguments/_test/_testmain.go:54 +0x20f
==================
1.030587504s
1.697008686s
1.932285314s
2.219673927s
2.769221406s
3.402550751s
3.734587528s
3.917955035s
4.398534118s
PASS
5.159202123s
5.42332977s
Found 1 data race(s)
FAIL    command-line-arguments  6.006s

echo $?
1