result.sh

% go version                                                                                                     [~/Desktop/go1.10]
go version devel +a99deed39b Mon Jan 8 18:06:27 2018 +0000 darwin/amd64

% go test -bench . -benchmem
goos: darwin
goarch: amd64

BenchmarkStringsBuilderWithoutGrow/10-4                   500000              2796 ns/op             160 B/op          5 allocs/op
BenchmarkStringsBuilderWithoutGrow/50-4                   200000              6942 ns/op             544 B/op          7 allocs/op
BenchmarkStringsBuilderWithoutGrow/100-4                  200000             10813 ns/op            1056 B/op          8 allocs/op
BenchmarkStringsBuilderWithoutGrow/200-4                  100000             18351 ns/op            2080 B/op          9 allocs/op
BenchmarkStringsBuilderWithoutGrow/500-4                   30000             39791 ns/op            7457 B/op         12 allocs/op

BenchmarkStringsBuilderWithGrow/10-4                     1000000              1898 ns/op              32 B/op          1 allocs/op
BenchmarkStringsBuilderWithGrow/50-4                      300000              5387 ns/op              32 B/op          1 allocs/op
BenchmarkStringsBuilderWithGrow/100-4                     200000              8699 ns/op              32 B/op          1 allocs/op
BenchmarkStringsBuilderWithGrow/200-4                     100000             15439 ns/op              32 B/op          1 allocs/op
BenchmarkStringsBuilderWithGrow/500-4                      50000             35775 ns/op              32 B/op          1 allocs/op

BenchmarkBytesBufferWithoutGrow/10-4                     1000000              2164 ns/op             160 B/op          2 allocs/op
BenchmarkBytesBufferWithoutGrow/50-4                      200000              6242 ns/op             752 B/op          4 allocs/op
BenchmarkBytesBufferWithoutGrow/100-4                     200000             10146 ns/op            1536 B/op          5 allocs/op
BenchmarkBytesBufferWithoutGrow/200-4                     100000             17278 ns/op            3168 B/op          6 allocs/op
BenchmarkBytesBufferWithoutGrow/500-4                      30000             39774 ns/op            6625 B/op          7 allocs/op

BenchmarkBytesBufferWithGrow/10-4                        1000000              2168 ns/op             160 B/op          2 allocs/op
BenchmarkBytesBufferWithGrow/50-4                         200000              5919 ns/op             320 B/op          2 allocs/op
BenchmarkBytesBufferWithGrow/100-4                        200000             10095 ns/op             528 B/op          2 allocs/op
BenchmarkBytesBufferWithGrow/200-4                        100000             19022 ns/op            1008 B/op          2 allocs/op
BenchmarkBytesBufferWithGrow/500-4                         30000             39827 ns/op            2160 B/op          2 allocs/op

PASS

stringsBuilder_vs_bytesBuffer.go

package main

import (
	"bytes"
	"fmt"
	"strings"
	"testing"
)

func stringsBuilder(b *testing.B, n int, grow bool) {
	for i := 0; i < b.N; i++ {
		var builder strings.Builder
		b.StopTimer()
		if grow {
			builder.Grow(n * 4)
		}
		b.StartTimer()
		for j := 0; j < n; j++ {
			fmt.Fprint(&builder, "TEST")
		}
		_ = builder.String()
	}
}

func bytesBuffer(b *testing.B, n int, grow bool) {
	for i := 0; i < b.N; i++ {
		var buf bytes.Buffer
		b.StopTimer()
		if grow {
			buf.Grow(n * 4)
		}
		b.StartTimer()
		for j := 0; j < n; j++ {
			fmt.Fprint(&buf, "TEST")
		}
		_ = buf.String()
	}
}

func BenchmarkStringsBuilderWithoutGrow(b *testing.B) {
	for _, n := range []int{10, 50, 100, 200, 500} {
		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {
			stringsBuilder(b, n, false)
		})
	}
}

func BenchmarkStringsBuilderWithGrow(b *testing.B) {
	for _, n := range []int{10, 50, 100, 200, 500} {
		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {
			stringsBuilder(b, n, true)
		})
	}
}

func BenchmarkBytesBufferWithoutGrow(b *testing.B) {
	for _, n := range []int{10, 50, 100, 200, 500} {
		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {
			bytesBuffer(b, n, false)
		})
	}
}

func BenchmarkBytesBufferWithGrow(b *testing.B) {
	for _, n := range []int{10, 50, 100, 200, 500} {
		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {
			bytesBuffer(b, n, true)
		})
	}
}