def test_length(self):
ll = DoublyLinkedList()
assert ll.length() == 0
# append and prepend operations increase length
ll.append('B')
assert ll.length() == 1
ll.prepend('A')
assert ll.length() == 2
ll.append('C')
assert ll.length() == 3
# delete operations decrease length
# assert(ll) == DoublyLinkedList(['A', 'B', 'C'])
assert(ll.head.data) == 'A'
assert(ll.head.prev) == None
assert(ll.head.next.prev.data) == 'A'
assert(ll.tail.data) == 'C'
assert(ll.tail.prev.data) == 'B'
assert(ll.tail.next) == None
ll.delete('B')
assert ll.length() == 2
ll.delete('C')
assert ll.length() == 1
ll.delete('A')
assert ll.length() == 0
def test_length(self):
dll = DoublyLinkedList()
assert dll.length() == 0
# append and prepend operations increase length
dll.append('B')
assert dll.length() == 1
dll.prepend('A')
assert dll.length() == 2
dll.append('C')
assert dll.length() == 3
# delete operations decrease length
dll.delete('B')
assert dll.length() == 2
dll.delete('C')
assert dll.length() == 1
dll.delete('A')
assert dll.length() == 0
