def test_insert_at_index(self):
dll = DoublyLinkedList()
dll.insert_at_index(0, 'S')
assert dll.get_at_index(0) == 'S'
assert dll.head.data == 'S'
assert dll.tail.data == 'S'
assert dll.size == 1
dll.insert_at_index(1, 'O')
assert dll.get_at_index(1) == 'O'
assert dll.head.data == 'S'
assert dll.tail.data == 'O'
assert dll.size == 2
dll.insert_at_index(1, 'X')
assert dll.get_at_index(1) == 'X'
assert dll.head.data == 'S'
assert dll.tail.data == 'O'
assert dll.size == 3
dll.insert_at_index(3, 'SSS')
assert dll.get_at_index(3) == 'SSS'
assert dll.head.data == 'S'
assert dll.tail.data == 'SSS'
assert dll.size == 4
def test_get_at_index(self):
dll = DoublyLinkedList(['A', 'B', 'C'])
assert dll.get_at_index(0) == 'A'
assert dll.get_at_index(1) == 'B'
assert dll.get_at_index(2) == 'C'