def test_delete(self):
ll = DoubleLinkedList(['A', 'B', 'C'])
ll.delete('A')
assert ll.head.data == 'B' # new head
assert ll.tail.data == 'C' # unchanged
assert ll.size == 2
ll.delete('C')
assert ll.head.data == 'B' # unchanged
assert ll.tail.data == 'B' # new tail
assert ll.size == 1
ll.delete('B')
assert ll.head is None # new head
assert ll.tail is None # new head
assert ll.size == 0
with self.assertRaises(ValueError):
ll.delete('X') # item not in list
def test_size(self):
ll = DoubleLinkedList()
assert ll.size == 0
# append and prepend operations increment size
ll.append('B')
assert ll.size == 1
ll.prepend('A')
assert ll.size == 2
ll.append('C')
assert ll.size == 3
# delete operations decrement size
ll.delete('B')
assert ll.size == 2
ll.delete('C')
assert ll.size == 1
ll.delete('A')
assert ll.size == 0
def test_length(self):
ll = DoubleLinkedList()
assert ll.length() == 0
# append and prepend operations increase length
ll.append('B')
assert ll.head.previous == None
assert ll.head.next == None
assert ll.tail.previous == None
assert ll.tail.next == None
assert ll.length() == 1
ll.prepend('A')
assert ll.head.previous == None
assert ll.head.next.data == 'B'
assert ll.tail.previous.data == 'A'
assert ll.tail.next == None
assert ll.length() == 2
ll.append('C')
assert ll.head.previous == None
assert ll.head.next.data == 'B'
assert ll.tail.previous.data == 'B'
assert ll.tail.next == None
assert ll.length() == 3
# delete operations decrease length
ll.delete('B')
assert ll.head.previous == None
assert ll.head.next.data == 'C'
assert ll.tail.previous.data == 'A'
assert ll.tail.next == None
assert ll.length() == 2
ll.delete('C')
assert ll.head.previous == None
assert ll.head.next == None
assert ll.tail.previous == None
assert ll.tail.next == None
assert ll.length() == 1
ll.delete('A')
assert ll.head == None
assert ll.head == None
assert ll.length() == 0