json_test.go

package main

import (
	"encoding/json"
	"io"
	"io/ioutil"
	"strings"
	"testing"
)

var data = `{"name":"eric"}`

type Person struct {
	Name string
}

func newReader() io.Reader {
	return strings.NewReader(data)
}

func BenchmarkReadFirst(b *testing.B) {
	b.ReportAllocs()
	for i := 0; i < b.N; i++ {
		var p Person
		data, err := ioutil.ReadAll(newReader())
		if err != nil {
			b.Fatal(err)
		}
		if err := json.Unmarshal(data, &p); err != nil {
			b.Fatal(err)
		}
	}
}

func BenchmarkDecoder(b *testing.B) {
	b.ReportAllocs()
	for i := 0; i < b.N; i++ {
		var p Person
		if err := json.NewDecoder(newReader()).Decode(&p); err != nil {
			b.Fatal(err)
		}
	}
}

out.txt

$ go test -bench=.
testing: warning: no tests to run
PASS
BenchmarkReadFirst-4	  500000	      2352 ns/op	    2368 B/op	       7 allocs/op
BenchmarkDecoder-4  	 1000000	      1667 ns/op	    1024 B/op	       7 allocs/op
ok  	_/home/eric/p/go/json	2.892s