def test_normal():
lst = [1, 2, 3, 4, 5]
link = list2link(lst)
assert find_kth_from_tail(link, 3).val == 3
def test_k0():
lst = [1, 2, 3, 4, 5]
link = list2link(lst)
assert find_kth_from_tail(link, 0).val == None
def test_none():
lst = []
link = list2link(lst)
assert find_kth_from_tail(link, 1).val == None
def test_kbiger_than_len():
lst = [1, 2, 3, 4, 5]
link = list2link(lst)
assert find_kth_from_tail(link, 6).val == None
def test_head():
lst = [1, 2, 3, 4, 5]
link = list2link(lst)
assert find_kth_from_tail(link, 5).val == 1