def test_pop_only_element():
ll = DoublyLinkedList()
for data in [0, "a", 1.5, [], {}, DoublyLinkedList()]:
ll.insert(0, data)
assert (not ll.is_empty())
assert (id(ll.peek_head()) == id(ll.peek_tail()))
actual = ll.pop(0)
assert (ll.is_empty())
assert (actual == data)
def test_insert_head():
ll = DoublyLinkedList()
for i in range(ITERS):
ll.insert_head(i)
assert (len(ll) == i + 1)
assert (ll.peek_head() == i)
