def test_normal():
root = list2link([1, 2, 3, 4, 5])
root_new = delete_node(root, root.next.next)
assert link2list(root_new) == [1, 2, 4, 5]
def test_head():
root = list2link([1, 2, 3, 4, 5])
root_new = delete_node(root, root)
assert link2list(root_new) == [2, 3, 4, 5]
def test_none():
root = list2link([])
root_new = delete_node(root, root)
assert link2list(root_new) == []