def test_prepend_adds_an_element_at_the_beginning_even_without_a_first_node(self):
linked = DoublyLinkedList()
node = Node(1000)
linked.prepend(node)
self.assertEqual(linked.as_list(), [1000])
self.assertIs(linked.first_node, node)
self.assertIs(linked.first_node.next, None)
self.assertIs(linked.first_node.previous, None)
def test_prepend_adds_an_element_at_the_beginning(self):
first_node = Node(100)
node = Node(1000)
linked = DoublyLinkedList(first_node)
linked.prepend(node)
self.assertEqual(linked.as_list(), [1000, 100])
self.assertIs(linked.first_node, node)
self.assertIs(linked.first_node.next, first_node)
self.assertIs(first_node.previous, node)
