def test_add_first():
ll = LinkedList()
ll.add_first(5)
assert ll.contains(5) == True
assert ll.at_index(5) == 0
ll.add_first(6)
assert ll.contains(6) == True
assert ll.at_index(6) == 0
def test_remove_last():
ll = LinkedList([1, 2, 3, 4, 5])
ll.remove_last()
assert ll.contains(5) == False
assert ll.at_index(5) == False
assert ll.length == 4
ll = LinkedList([1])
ll.remove_last()
assert ll.length == 0
assert ll.contains(1) == False
assert ll.at_index(1) == False
def test_add_last():
ll = LinkedList()
ll.add_last(3)
assert ll.contains(3) == True
assert ll.at_index(3) == 0
ll.add_last(4)
assert ll.contains(4) == True
assert ll.at_index(4) == 1
ll.add_last(5)
assert ll.contains(5) == True
assert ll.at_index(5) == 2
def test_add_at():
ll = LinkedList()
ll.add_at(5, 0)
assert ll.contains(5) == True
assert ll.at_index(5) == 0
ll_two = LinkedList([1, 23, 4, 5, 6, 78])
ll_two.add_at(12, 0)
assert ll_two.contains(12) == True
assert ll_two.at_index(12) == 0
ll_two.add_at(21, 3)
assert ll_two.contains(21) == True
assert ll_two.at_index(21) == 3
