def test_insert_at_index(self):
dll = DoublyLinkedList()
dll.insert_at_index(0, 'B')
assert dll.head.data == 'B'
assert dll.tail.data == 'B'
assert dll.size == 1
dll.insert_at_index(1, 'C')
assert dll.head.data == 'B'
assert dll.tail.data == 'C'
assert dll.size == 2
dll.insert_at_index(0, 'A')
assert dll.head.data == 'A'
assert dll.tail.data == 'C'
assert dll.size == 3
with self.assertRaises(ValueError):
dll.insert_at_index(4, 'D')
dll.insert_at_index(-1, 'E')
def test_insert_at_index(self):
ll = DoublyLinkedList()
ll.insert_at_index(0, 'B') # append('B')
assert ll.head.data == 'B' # new head (at index 0)
assert ll.tail.data == 'B' # new tail (at index 0)
assert ll.size == 1
ll.insert_at_index(0, 'A') # prepend('A')
assert ll.head.data == 'A' # new head (at index 0)
assert ll.tail.data == 'B' # unchanged (now at index 1)
assert ll.size == 2
ll.insert_at_index(2, 'D') # append('D')
assert ll.head.data == 'A' # unchanged (at index 0)
assert ll.tail.data == 'D' # new tail (now at index 2)
assert ll.size == 3
ll.insert_at_index(2, 'C') # insert 'C' between 'B' and 'D'
assert ll.head.data == 'A' # unchanged (at index 0)
assert ll.tail.data == 'D' # unchanged (now at index 3)
assert ll.size == 4
with self.assertRaises(ValueError):
ll.insert_at_index(5, 'X') # index too high
with self.assertRaises(ValueError):
ll.insert_at_index(-1, 'Y') # index too low
