Accessing a benchmark's result

I've seen there is a struct testing.BenchmarkResult in Go to accesss the result of a benchmark but I found very little documentation or examples to help me use it.

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So far I have only been benchmarking my functions like this:

func BenchmarkMyFunction(b *testing.B) {
   // call to myFunction
}

And then running:

go test -bench=".*"

Here the results are printed to the console but I'd like to store them in a separate file. How can I use the BenchmarkResult type to do this?

For example:

package main
import (
	"fmt"
	"testing"
	"time"
)
func Add(a, b int) int {
	time.Sleep(10 * time.Microsecond) // Just to make the test take some time
	return a + b
}
func BenchAdd(b *testing.B) {
	for i := 0; i < b.N; i++ {
		_ = Add(1, 2)
	}
}
func main() {
	res := testing.Benchmark(BenchAdd)
	fmt.Printf("%s\n%#[1]v\n", res)
}

Produces:

  120000	     10000 ns/op
testing.BenchmarkResult{N:120000, T:1200000000, Bytes:0, MemAllocs:0x0, MemBytes:0x0, Extra:map[string]float64{}}

Playground.

You can easily write these results out to a file using ioutil.WriteFile.
Playground w/ WriteFile.