Added ListNodeTestHelper class

Author: ignacio-chiazzo

utilsClasses/ListNodeTestHelper.js

@@ -1,13 +1,12 @@
 const assert = require('assert');
 
 var assertList = function(list, expectedArr) {
-  assert.strictEqual(list.length(), expectedArr.length);
+  const listlength = list ? list.length() : 0;
+  assert.strictEqual(listlength, expectedArr.length);
   for(var i = 0; i < expectedArr.length; i++) {
     assert.strictEqual(list.val, expectedArr[i]);
     list = list.next;
   }
-
-  assert(list)
 }
 
 module.exports.assertList = assertList;