How to rewrite rand.Seed(1) when migrate from go 1.13 to 1.20.1?

File bench.go

package bench

import "os"

func FileLen(f string, bufsize int) (int, error) {
	file, err := os.Open(f)
	if err != nil {
		return 0, err
	}
	defer file.Close()
	count := 0
	buf := make([]byte, bufsize)
	for {
		num, err := file.Read(buf)
		count += num
		if err != nil {
			break
		}
	}
	return count, nil
}

File bench_test.go

package bench

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

func TestMain(m *testing.M) {
	makeData()
	exitVal := m.Run()
	os.Remove("testdata/data.txt")
	os.Exit(exitVal)
}

// makeData makes our data file for us. Rather than checking in a large file, we recreate it for the test.
// By setting the random seed to the same value every time, we ensure that we generate the same file every time.
// This random seed generates a file that's 65,204 bytes long.
func makeData() {
	file, err := os.Create("testdata/data.txt")
	if err != nil {
		panic(err)
	}
	defer file.Close()

	rand.Seed(1)
	for i := 0; i < 10000; i++ {
		data := makeWord(rand.Intn(10) + 1)
		file.Write(data)
	}
}

func makeWord(l int) []byte {
	out := make([]byte, l+1)
	for i := 0; i < l; i++ {
		out[i] = 'a' + byte(rand.Intn(26))
	}
	out[l] = '\n'
	return out
}

func TestFileLen(t *testing.T) {
	result, err := FileLen("testdata/data.txt", 1)
	if err != nil {
		t.Fatal(err)
	}
	if result != 65204 {
		t.Error("Expected 65204, got", result)
	}
}

var blackhole int

func BenchmarkFileLen1(b *testing.B) {
	for i := 0; i < b.N; i++ {
		result, err := FileLen("testdata/data.txt", 1)
		if err != nil {
			b.Fatal(err)
		}
		blackhole = result
	}
}

func BenchmarkFileLen(b *testing.B) {
	for _, v := range []int{1, 10, 100, 1000, 10000, 100000} {
		b.Run(fmt.Sprintf("FileLen-%d", v), func(b *testing.B) {
			for i := 0; i < b.N; i++ {
				result, err := FileLen("testdata/data.txt", v)
				if err != nil {
					b.Fatal(err)
				}
				blackhole = result
			}
		})
	}
}

https://github.com/learning-go-book-2evy/test_examples/blob/master/bench/bench_test.go#L27

I tried change to rand.NewSource(1) but test fail. How to rewrite rand.Seed(1) when migrate from go 1.13 to 1.20.1?

As of Go 1.20.1 there is an error in the documentation for rand.Rand. It reads

> Programs that need a specific result sequence should use NewRand(NewSource(seed)).

The constructor for the PRNG is called New, not NewRand.

To replace uses of the global seed, pass the return value of rand.NewSource to rand.New to obtain a PRNG. This PRNG then has the same API as the package level functions:

package main

import "math/rand"

func main() {
	rng := rand.New(rand.NewSource(1))
	n := rng.Intn(10) + 1 // instead of rand.Intn
	_ = n
}

Changing the original to the following will pass the benchmark tests:

func makeData() {
	file, err := os.Create("testdata/data.txt")
	if err != nil {
		panic(err)
	}
	defer file.Close()

	r := rand.New(rand.NewSource(1))
	for i := 0; i < 10000; i++ {
		data := makeWord(r.Intn(10)+1, r)
		file.Write(data)
	}
}

func makeWord(l int, r *rand.Rand) []byte {
	out := make([]byte, l+1)
	for i := 0; i < l; i++ {
		out[i] = 'a' + byte(r.Intn(26))
	}
	out[l] = '\n'
	return out
}