def test_insert_2(self):
linked_list = LinkedList()
linked_list.add_in_tail(self.n1)
linked_list.add_in_tail(self.n3)
linked_list.insert(self.n3, self.n6)
self.assertEqual(linked_list.head, self.n1)
self.assertEqual(linked_list.tail, self.n6)
self.assertEqual(self.n3.next, self.n6)
self.assertEqual(self.n6.next, None)
self.assertEqual(self.n6.prev, self.n3)
def test_insert_1(self):
linked_list = LinkedList()
linked_list.insert(None, self.n6)
self.assertEqual(linked_list.head, self.n6)
self.assertEqual(linked_list.tail, self.n6)