Add utils.randomHex unit test

test/utils.randomHex.js

@@ -0,0 +1,25 @@
+var chai = require('chai');
+var utils = require('../packages/web3-utils');
+
+var assert = chai.assert;
+
+// Expect 2 chars per bytes plus `0x` prefix
+var tests = [
+    { value:  0, expected: { prefix: '0x', type: 'string', length: 2 }},
+    { value: 15, expected: { prefix: '0x', type: 'string', length: 32 }},
+    { value: 16, expected: { prefix: '0x', type: 'string', length: 34 }}
+];
+
+describe('lib/utils/utils', function () {
+    describe('randomHex', function () {
+        tests.forEach(function (test) {
+            it('should turn ' + test.value + ' to ' + test.expected, function () {
+                var result = utils.randomHex(test.value);
+
+                assert.strictEqual(typeof result, test.expected.type);
+                assert.strictEqual(result.slice(0,2), test.expected.prefix);
+                assert.strictEqual(result.length, test.expected.length);
+            });
+        });
+    });
+});