diff --git a/pkg/stringutil/stringutil.go b/pkg/stringutil/stringutil.go
new file mode 100644
index 000000000..7f6aeb8a6
--- /dev/null
+++ b/pkg/stringutil/stringutil.go
@@ -0,0 +1,54 @@
+// Copyright 2016 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package stringutil
+
+import "math/rand"
+
+const (
+	chars = "abcdefghijklmnopqrstuvwxyz0123456789"
+)
+
+// UniqueStrings retruns a slice of randomly generated unique strings.
+func UniqueStrings(maxlen uint, n int) []string {
+	exist := make(map[string]bool)
+	ss := make([]string, 0)
+
+	for len(ss) < n {
+		s := randomString(maxlen)
+		if !exist[s] {
+			exist[s] = true
+			ss = append(ss, s)
+		}
+	}
+
+	return ss
+}
+
+// RandomStrings retruns a slice of randomly generated strings.
+func RandomStrings(maxlen uint, n int) []string {
+	ss := make([]string, 0)
+	for i := 0; i < n; i++ {
+		ss = append(ss, randomString(maxlen))
+	}
+	return ss
+}
+
+func randomString(l uint) string {
+	s := make([]byte, l)
+	for i := 0; i < int(l); i++ {
+		s[i] = chars[rand.Intn(len(chars))]
+	}
+	return string(s)
+}
diff --git a/tools/functional-tester/etcd-runner/watcher.go b/tools/functional-tester/etcd-runner/watcher.go
index 492838384..39dc856cb 100644
--- a/tools/functional-tester/etcd-runner/watcher.go
+++ b/tools/functional-tester/etcd-runner/watcher.go
@@ -18,11 +18,11 @@ import (
 	"context"
 	"fmt"
 	"log"
-	"math/rand"
 	"sync"
 	"time"
 
 	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/pkg/stringutil"
 	"golang.org/x/time/rate"
 )
 
@@ -40,8 +40,8 @@ func performWatchOnPrefixes(ctx context.Context, getClient getClientFunc, round
 	reqRate := 30                   // put request per second
 	keyPrePrefix := 30              // max number of keyPrePrefixs for put operation
 
-	prefixes := generateUniqueKeys(5, noOfPrefixes)
-	keys := generateRandomKeys(10, keyPrePrefix)
+	prefixes := stringutil.UniqueStrings(5, noOfPrefixes)
+	keys := stringutil.RandomStrings(10, keyPrePrefix)
 
 	roundPrefix := fmt.Sprintf("%16x", round)
 
@@ -167,43 +167,3 @@ func getWithRetry(client *clientv3.Client, ctx context.Context, key string) *cli
 		}
 	}
 }
-
-func generateUniqueKeys(maxstrlen uint, keynos int) []string {
-	keyMap := make(map[string]bool)
-	keys := make([]string, 0)
-	count := 0
-	key := ""
-	for {
-		key = generateRandomKey(maxstrlen)
-		_, ok := keyMap[key]
-		if !ok {
-			keyMap[key] = true
-			keys = append(keys, key)
-			count++
-			if len(keys) == keynos {
-				break
-			}
-		}
-	}
-	return keys
-}
-
-func generateRandomKeys(maxstrlen uint, keynos int) []string {
-	keys := make([]string, 0)
-	key := ""
-	for i := 0; i < keynos; i++ {
-		key = generateRandomKey(maxstrlen)
-		keys = append(keys, key)
-	}
-	return keys
-}
-
-func generateRandomKey(strlen uint) string {
-	chars := "abcdefghijklmnopqrstuvwxyz0123456789"
-	result := make([]byte, strlen)
-	for i := 0; i < int(strlen); i++ {
-		result[i] = chars[rand.Intn(len(chars))]
-	}
-	key := string(result)
-	return key
-}