generate random strings

random.go

package random

import (
	"crypto/rand"
	"math/big"
)

const (
	Length = 5
	Number = "0123456789"
	Letter = "abcdefghijklmnopqrstuvwxyz"
)

const (
	all = Number + Letter
)

func New() string {
	var ran string

	for i := 0; i < Length; i++ {
		ind, err := rand.Int(rand.Reader, big.NewInt(int64(len(all))))
		if err != nil {
			panic(err)
		}

		ran += string(all[ind.Int64()])
	}

	return ran
}

random_test.go

package random

import (
	"sync"
	"testing"
)

func Test_Random_New(t *testing.T) {
	mut := sync.Mutex{}
	see := map[string]struct{}{}

	for i := 0; i < 1000; i++ {
		go func() {
			a := New()
			b := New()

			if a == "" || b == "" {
				panic("random strings must not be empty")
			}

			if len(a) != Length || len(b) != Length {
				panic("random strings must have the right length")
			}

			if a == b {
				panic("random strings must be unique")
			}

			{
				mut.Lock()
			}

			{
				_, exi := see[a]
				if exi {
					panic("random strings must not be duplicated")
				}

				see[a] = struct{}{}
			}

			{
				_, exi := see[b]
				if exi {
					panic("random strings must not be duplicated")
				}

				see[b] = struct{}{}
			}

			{
				mut.Unlock()
			}
		}()
	}
}