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) == []