diff --git a/test/util_test.js b/test/util_test.js
new file mode 100644
index 0000000..78b487c
--- /dev/null
+++ b/test/util_test.js
@@ -0,0 +1,36 @@
+var util = require('../lib/util');
+var assert = require('assert');
+
+describe('Util module test', function() {
+
+    var a = util.Util;
+    
+    describe('static rjust() function', function() {
+        it("should set the init num length to n", function() {
+            assert.equal("00123", a.rjust(123, 5));
+        });
+    });
+
+    describe('static arr_rjust() function', function() {
+        it("should set the init arr length to n", function() {
+            let arr = [1, "", "3"];
+            let arr_wanted_length = 4;
+            assert.equal(arr_wanted_length, a.arr_rjust(arr, 4).length);
+        });
+    });
+
+    describe('static byte_secret() function', function() {
+        it("should transfer the secret to byte", function() {
+            let secret = "J22U6B3WIWRRBTAV";
+            assert.equal("NµO\u0007vE£\u0010Ì\u0015", a.byte_secret(secret));
+        });
+    });
+
+    describe('static int_to_bytestring() function', function() {
+        it("should transfer the input counter or time to bytestring", function() {
+            let input = 49957590;
+            assert.equal("\u0000\u0000\u0000\u0000\u0002úJÖ", a.int_to_bytestring(input));
+        });
+    });    
+
+});