diff --git a/random/random.go b/random/random.go
index bceca50..9d7dc5f 100644
--- a/random/random.go
+++ b/random/random.go
@@ -329,6 +329,7 @@ func UUIdV4() (string, error) {
 }
 
 // RandNumLen 生成一个长度为len的随机数
+// Play: https://go.dev/play/p/jpIalcD5rMo
 func RandNumLen(len int) int {
 	m := int(math.Pow10(len) - 1)
 	i := int(math.Pow10(len - 1))
diff --git a/random/random_test.go b/random/random_test.go
index f7df09d..9f0f5e0 100644
--- a/random/random_test.go
+++ b/random/random_test.go
@@ -3,6 +3,7 @@ package random
 import (
 	"reflect"
 	"regexp"
+	"strconv"
 	"testing"
 
 	"github.com/duke-git/lancet/v2/internal"
@@ -361,3 +362,9 @@ func TestRandBoolSlice(t *testing.T) {
 		}
 	})
 }
+func TestRandNumLen(t *testing.T) {
+	t.Parallel()
+	randi := RandNumLen(6)
+	assert := internal.NewAssert(t, "TestRandNumLen")
+	assert.Equal(6, len(strconv.Itoa(randi)))
+}