def test_push_first_a_few_elements(self):
l = DoubleLinkedList()
l.push_first(1)
l.push_first(2)
l.push_first(3)
self.assertEqual(list(l), [3, 2, 1])
def test_push_first_one_element(self):
l = DoubleLinkedList()
l.push_first(1)
self.assertEqual(list(l), [1])