diff --git a/src/test/java/com/alibaba/ttl/perf/Utils.java b/src/test/java/com/alibaba/ttl/perf/Utils.java
deleted file mode 100644
index fe717f932ef7082d433e33ef409dae18bdcf5e7c..0000000000000000000000000000000000000000
--- a/src/test/java/com/alibaba/ttl/perf/Utils.java
+++ /dev/null
@@ -1,32 +0,0 @@
-package com.alibaba.ttl.perf;
-
-import java.util.Random;
-
-/**
- * @author Jerry Lee (oldratlee at gmail dot com)
- */
-public class Utils {
-    private static Random random = new Random();
-
-    private static String bytes2Hex(byte[] bytes) {
-        StringBuilder sb = new StringBuilder(1024);
-        for (byte b : bytes) {
-            String s = Integer.toHexString(b & 0xFF);
-            sb.append((s.length() == 1) ? "0" + s : s);
-        }
-        return sb.toString();
-    }
-
-    private static byte[] getRandomBytes() {
-        byte[] bytes = new byte[1024];
-        random.nextBytes(bytes);
-        return bytes;
-    }
-
-    public static String getRandomString() {
-        return bytes2Hex(getRandomBytes());
-    }
-
-    private Utils() {
-    }
-}
diff --git a/src/test/java/com/alibaba/ttl/perf/Utils.kt b/src/test/java/com/alibaba/ttl/perf/Utils.kt
new file mode 100644
index 0000000000000000000000000000000000000000..71ba1e76b911d0fc310d241650c664478e52b8ba
--- /dev/null
+++ b/src/test/java/com/alibaba/ttl/perf/Utils.kt
@@ -0,0 +1,25 @@
+package com.alibaba.ttl.perf
+
+import java.util.*
+
+private val random = Random()
+
+internal fun bytes2Hex(bytes: ByteArray): String {
+    val sb = StringBuilder(1024)
+    for (b in bytes) {
+        val s = Integer.toHexString(b.toInt() and 0xFF)
+        sb.append(if (s.length == 1) "0$s" else s)
+    }
+    return sb.toString()
+}
+
+internal fun getRandomBytes(): ByteArray {
+    val bytes = ByteArray(1024)
+    random.nextBytes(bytes)
+    return bytes
+}
+
+internal fun getRandomString(): String {
+    return bytes2Hex(getRandomBytes())
+}
+
diff --git a/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_ThreadLocal_NoRemove.kt b/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_ThreadLocal_NoRemove.kt
index cb667ea3173c0cc347dbcb43b11979632de1c118..098e9264f1a9bab28d9bd4e5509dde41e07d5d31 100644
--- a/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_ThreadLocal_NoRemove.kt
+++ b/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_ThreadLocal_NoRemove.kt
@@ -2,7 +2,7 @@
 
 package com.alibaba.ttl.perf.memoryleak
 
-import com.alibaba.ttl.perf.Utils
+import com.alibaba.ttl.perf.getRandomString
 
 /**
  * @author Jerry Lee (oldratlee at gmail dot com)
@@ -11,7 +11,7 @@ fun main(args: Array<String>) {
     var counter: Long = 0
     while (true) {
         val threadLocal = ThreadLocal<String>()
-        threadLocal.set(Utils.getRandomString())
+        threadLocal.set(getRandomString())
 
         if (counter % 1000 == 0L)
             System.out.printf("%05dK%n", counter / 1000)
diff --git a/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_TransmittableThreadLocal_NoRemove.kt b/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_TransmittableThreadLocal_NoRemove.kt
index 64eb5ecb1ed69e7507ef987a36b162573ac2d843..6f31b9ada7ae6092904bb832fb60fcc0bcf6f97a 100644
--- a/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_TransmittableThreadLocal_NoRemove.kt
+++ b/src/test/java/com/alibaba/ttl/perf/memoryleak/NoMemoryLeak_TransmittableThreadLocal_NoRemove.kt
@@ -3,7 +3,7 @@
 package com.alibaba.ttl.perf.memoryleak
 
 import com.alibaba.ttl.TransmittableThreadLocal
-import com.alibaba.ttl.perf.Utils
+import com.alibaba.ttl.perf.getRandomString
 
 /**
  * @author Jerry Lee (oldratlee at gmail dot com)
@@ -12,7 +12,7 @@ fun main(args: Array<String>) {
     var counter: Long = 0
     while (true) {
         val threadLocal = TransmittableThreadLocal<String>()
-        threadLocal.set(Utils.getRandomString())
+        threadLocal.set(getRandomString())
 
         if (counter % 1000 == 0L)
             System.out.printf("%05dK%n", counter / 1000)
diff --git a/src/test/java/com/alibaba/ttl/perf/tps/CreateThreadLocalInstanceTps.kt b/src/test/java/com/alibaba/ttl/perf/tps/CreateThreadLocalInstanceTps.kt
index 9ffb718fd450b056b49b58df3afcc7eed08be769..16bf99c3a7bed49357f0d0e57e48036bc4818753 100644
--- a/src/test/java/com/alibaba/ttl/perf/tps/CreateThreadLocalInstanceTps.kt
+++ b/src/test/java/com/alibaba/ttl/perf/tps/CreateThreadLocalInstanceTps.kt
@@ -2,7 +2,7 @@
 
 package com.alibaba.ttl.perf.tps
 
-import com.alibaba.ttl.perf.Utils
+import com.alibaba.ttl.perf.getRandomString
 
 /**
  * @author Jerry Lee (oldratlee at gmail dot com)
@@ -12,7 +12,7 @@ fun main(args: Array<String>) {
 
     tpsCounter.setAction(Runnable {
         val threadLocal = ThreadLocal<String>()
-        threadLocal.set(Utils.getRandomString())
+        threadLocal.set(getRandomString())
     })
 
     while (true) {
diff --git a/src/test/java/com/alibaba/ttl/perf/tps/CreateTransmittableThreadLocalInstanceTps.kt b/src/test/java/com/alibaba/ttl/perf/tps/CreateTransmittableThreadLocalInstanceTps.kt
index f40cc2644da1d1bdd9813259bce40d2834e176cf..3d6764ebbecec935be926ab63875025adbf27837 100644
--- a/src/test/java/com/alibaba/ttl/perf/tps/CreateTransmittableThreadLocalInstanceTps.kt
+++ b/src/test/java/com/alibaba/ttl/perf/tps/CreateTransmittableThreadLocalInstanceTps.kt
@@ -3,7 +3,7 @@
 package com.alibaba.ttl.perf.tps
 
 import com.alibaba.ttl.TransmittableThreadLocal
-import com.alibaba.ttl.perf.Utils
+import com.alibaba.ttl.perf.getRandomString
 
 /**
  * @author Jerry Lee (oldratlee at gmail dot com)
@@ -13,7 +13,7 @@ fun main(args: Array<String>) {
 
     tpsCounter.setAction(Runnable {
         val threadLocal = TransmittableThreadLocal<String>()
-        threadLocal.set(Utils.getRandomString())
+        threadLocal.set(getRandomString())
     })
 
     while (true) {
diff --git a/src/test/java/com/alibaba/ttl/perf/tps/TpsCounter.kt b/src/test/java/com/alibaba/ttl/perf/tps/TpsCounter.kt
index 73c1c85499d1c67947354eb13f0723599c616dea..e3d83e24af6a5ba7d19c9b9a7551b24030a672bf 100644
--- a/src/test/java/com/alibaba/ttl/perf/tps/TpsCounter.kt
+++ b/src/test/java/com/alibaba/ttl/perf/tps/TpsCounter.kt
@@ -1,12 +1,11 @@
 package com.alibaba.ttl.perf.tps
 
+import org.junit.Assert.fail
 import java.util.concurrent.ExecutorService
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicLong
 
-import org.junit.Assert.fail
-
 /**
  * @author Jerry Lee (oldratlee at gmail dot com)
  */
diff --git a/src/test/java/com/alibaba/ttl/user_api_test/TransmittableThreadLocal_Transmitter_UserTest.kt b/src/test/java/com/alibaba/ttl/user_api_test/TransmittableThreadLocal_Transmitter_UserTest.kt
index b96126ce78a2938df7e0eb0af3c819cdcf6f1f98..5b3e396fe674d8d4f89030b0bc57cbb51216c7f6 100644
--- a/src/test/java/com/alibaba/ttl/user_api_test/TransmittableThreadLocal_Transmitter_UserTest.kt
+++ b/src/test/java/com/alibaba/ttl/user_api_test/TransmittableThreadLocal_Transmitter_UserTest.kt
@@ -108,6 +108,7 @@ class TransmittableThreadLocal_Transmitter_UserTest {
         }
 
         @AfterClass
+        @Suppress("unused")
         fun afterClass() {
             executorService.shutdown()
             executorService.awaitTermination(100, TimeUnit.MILLISECONDS)