public void PushBack()
        {
            DLinkedList<int> list = new DLinkedList<int>();
            int expectedResult=5, result;


            list.PushBack(expectedResult);
            result = list.OnBack();

            Assert.AreEqual(expectedResult,result);

        }
        public void PopFront()
        {
            DLinkedList<int> list = new DLinkedList<int>();
            int expectedResult = 1, result;

            list.PushFront(1);
            list.PushBack(2);
            list.PushFront(3);
            list.PopFront();

            result = list.OnFront();

            Assert.AreEqual(expectedResult, result);
        }
        public void Clear()
        {
            DLinkedList<string> list = new DLinkedList<string>();
            
            list.PushBack("a");
            list.PushBack("b");
            list.PushBack("c");
            list.PushBack("d");
            list.PushBack("e");
            list.PushBack("f");
            list.Clear();

            Assert.IsTrue(list.IsEmpty());
        }
        public void GetEnumerator()
        {
            DLinkedList<string> list = new DLinkedList<string>();
            string result="", expectedResult = "abcdef";
            
            list.PushBack("a");
            list.PushBack("b");
            list.PushBack("c");
            list.PushBack("d");
            list.PushBack("e");
            list.PushBack("f");

            foreach (var s in list)
            {
                result += s;
            }

            Assert.AreEqual(expectedResult,result);
        }