Add more test cases to rand string gen

* Exercise random string generation by adding larger test cases
* wrap random number generation with a mutex because math/rand isn't goroutine safe
Signed-off-by: bryanl <bryanliles@gmail.com>

pkg/util/strings/rand.go

@@ -28,14 +28,20 @@ const (
 	letterIdxMax  = 63 / letterIdxBits   // number of letter indices fitting in 63 bits
 )
 
-var randSrc = rand.NewSource(time.Now().UnixNano())
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
 
 // Rand generates a random string of lower and upper case letters n characters long.
 func Rand(n int) string {
+	if n < 1 {
+		return ""
+	}
+
 	b := make([]byte, n)
-	for i, cache, remain := n-1, randSrc.Int63(), letterIdxMax; i >= 0; {
+	for i, cache, remain := n-1, rand.Int63(), letterIdxMax; i >= 0; {
 		if remain == 0 {
-			cache, remain = randSrc.Int63(), letterIdxMax
+			cache, remain = rand.Int63(), letterIdxMax
 		}
 		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
 			b[i] = letterBytes[idx]
@@ -50,10 +56,14 @@ func Rand(n int) string {
 
 // LowerRand generates a random string of lower case letters n characters long.
 func LowerRand(n int) string {
+	if n < 1 {
+		return ""
+	}
+
 	b := make([]byte, n)
-	for i, cache, remain := n-1, randSrc.Int63(), letterIdxMax; i >= 0; {
+	for i, cache, remain := n-1, rand.Int63(), letterIdxMax; i >= 0; {
 		if remain == 0 {
-			cache, remain = randSrc.Int63(), letterIdxMax
+			cache, remain = rand.Int63(), letterIdxMax
 		}
 		if idx := int(cache & letterIdxMask); idx < len(letterLowerBytes) {
 			b[i] = letterLowerBytes[idx]

pkg/util/strings/rand_test.go

@@ -16,6 +16,7 @@
 package strings
 
 import (
+	"fmt"
 	"regexp"
 	"testing"
 
@@ -23,19 +24,37 @@ import (
 )
 
 func TestRand(t *testing.T) {
-	got := Rand(5)
+	for i := 1; i < 45; i++ {
+		t.Run(fmt.Sprintf("Rand(%d)", i), func(t *testing.T) {
+			got := Rand(i)
 
-	assert.Len(t, got, 5)
+			assert.Len(t, got, i)
 
-	re := regexp.MustCompile(`^[A-Za-z]{5}$`)
-	assert.True(t, re.MatchString(got))
+			re := regexp.MustCompile(fmt.Sprintf(`^[A-Za-z]{%d}$`, i))
+			assert.True(t, re.MatchString(got))
+		})
+	}
+}
+
+func TestRand_negative(t *testing.T) {
+	got := Rand(-1)
+	assert.Len(t, got, 0)
 }
 
 func TestLowerRand(t *testing.T) {
-	got := LowerRand(5)
+	for i := 1; i < 45; i++ {
+		t.Run(fmt.Sprintf("LowerRand(%d)", i), func(t *testing.T) {
+			got := LowerRand(i)
 
-	assert.Len(t, got, 5)
+			assert.Len(t, got, i)
+
+			re := regexp.MustCompile(fmt.Sprintf(`^[a-z]{%d}$`, i))
+			assert.True(t, re.MatchString(got))
+		})
+	}
+}
 
-	re := regexp.MustCompile(`^[a-z]{5}$`)
-	assert.True(t, re.MatchString(got))
+func TestLowerRand_negative(t *testing.T) {
+	got := LowerRand(-1)
+	assert.Len(t, got, 0)
 }