def test_insert_after():
l = DoubleLinkedList()
l.append(5)
l.append(7)
l.append(9)
l.insert_after(l.front, 13)
assert l.front.next.value == 13
assert_contains(l, [5, 13, 7, 9])
def test_insert_after_2():
l = DoubleLinkedList()
l.append(5)
l.insert_after(l.front, 13)
assert l.end.value == 13
assert_contains(l, [5, 13])