How to test Go function execution time using standard lib

Question

I've written the following function that when used with Defer will surely do the trick but is there something in standard library I could use for this? I'm looking something similar to Python timeit which I could use directly from the shell?

package main

import (
    "fmt"
    "time"
)

func main() {
    defer timeTrack(time.Now(), "looptest")
    nums := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
    var m []int
    for n := range nums {
        if n%2 == 0 {
            m = append(m, n)
        }
    }
}

func timeTrack(start time.Time, name string) {
    elapsed := time.Since(start)
    fmt.Printf("%s took %s", name, elapsed)
}

Answer 1

Use the Go testing package. For example,

main.go:

package main

func doStuff() {
    nums := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
    var m []int
    for n := range nums {
        if n%2 == 0 {
            m = append(m, n)
        }
    }
}

func main() {
    doStuff()
}

main_test.go:

package main

import "testing"

func BenchmarkStuff(b *testing.B) {
    for i := 0; i < b.N; i++ {
        doStuff()
    }
}

Output:

$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: main
BenchmarkStuff-4    5000000    276 ns/op    120 B/op    4 allocs/op

---

Using the information from the benchmark, you can improve performance. Reduce the number and size of allocations by using an estimate to initialize slice m.

func doStuff() {
    nums := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
    m := make([]int, 0, len(nums)/2+1)
    for n := range nums {
        if n%2 == 0 {
            m = append(m, n)
        }
    }
}

Output:

$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: main
BenchmarkStuff-4    20000000    83.1 ns/op    48 B/op    1 allocs/op

Answer 2

You can use testing

func BenchmarkFoo(b *testing.B) {
    for i := 0; i < b.N; i++ {
        Foo()
    }
}