def test_linked_list_insert_after():
ll = LinkedList()
ll.head = Node(1)
ll.head.next = Node(2)
ll.insert_after(1, 4)
assert ll.head.next.value == 4
assert ll.head.next.next.value == 2
def test_linked_list_insert_after():
"""Test a value can be inserted after a value already in the linked list."""
linked_list = LinkedList()
value = 1
linked_list.insert(value)
new_value = 2
linked_list.insert_after(value, new_value)
assert linked_list.head.next.value == new_value
assert linked_list.head.next.next == None
newer_value = 3
linked_list.insert_after(value, newer_value)
assert linked_list.head.next.value == newer_value
assert linked_list.head.next.next.value == new_value
assert linked_list.head.next.next.next == None