public void MergeTwoLists_FirstCase_True()
        {
            var list1 = new ListNode(3);
            var node3 = new ListNode(3);
            var node5 = new ListNode(5);

            list1.next = node3;
            node3.next = node5;

            var list2 = new ListNode(1);
            var node1 = new ListNode(1);
            var node2 = new ListNode(2);
            var node6 = new ListNode(6);

            list2.next = node1;
            node1.next = node2;
            node2.next = node6;

            var expectedOutput = "1,1,2,3,3,5,6";
            var output         = _linkedListService.MergeTwoLists(list1, list2);
            var actualOutput   = _linkedListService.GetListValues(output);

            Assert.Equal(expectedOutput, actualOutput);
        }