def test_len_three() -> None:
"""Test LinkedList.__len__ on a linked list of length 3."""
lst = LinkedList()
node1 = _Node(10)
node2 = _Node(20)
node3 = _Node(30)
node1.next = node2
node2.next = node3
lst._first = node1
assert len(lst) == 3
def test_contains_doctest() -> None:
"""Test LinkedList.__contains__ on the given doctest."""
lst = LinkedList()
node1 = _Node(1)
node2 = _Node(2)
node3 = _Node(3)
node1.next = node2
node2.next = node3
lst._first = node1
assert 2 in lst
assert not (4 in lst)
def test_append_one() -> None:
"""Test LinkedList.append on a list of length 1."""
lst = LinkedList()
lst._first = _Node(1)
lst.append(2)
assert lst._first.next.item == 2
def test_append_empty() -> None:
"""Test LinkedList.append on an empty list."""
lst = LinkedList()
lst.append(1)
assert lst._first.item == 1
def test_len_empty() -> None:
"""Test LinkedList.__len__ for an empty linked list."""
lst = LinkedList()
assert len(lst) == 0