def test_node_delete(self): # Failure message: # Your `Node.delete` method did not work as expected node_1 = ListNode(3) node_2 = ListNode(4) node_3 = ListNode(5) node_1.next = node_2 node_2.next = node_3 node_2.prev = node_1 node_3.prev = node_2 node_2.delete() self.assertEqual(node_1.next, node_3) self.assertEqual(node_3.prev, node_1)