def test_find_from_k():
    mammals = LinkedList()
    mammals.add('orca')
    mammals.add('beluga')
    mammals.add('porpoise')
    mammals.add('otter')
    mammals.add('seal')

    assert mammals.find_from_end(2) == 'porpoise'
    assert mammals.find_from_end(4) == 'orca'
    assert mammals.find_from_end(5) is None
def test_find_from_end_exception():
    fruits = LinkedList()
    fruits.insert('apples')
    fruits.insert('bananas')
    fruits.insert('pears')
    fruits.insert('grapes')
    actual = fruits.find_from_end(5)
    assert 'exception' == actual
def test_find_from_end_second():
    fruits = LinkedList()
    fruits.insert('apples')
    fruits.insert('bananas')
    fruits.insert('pears')
    fruits.insert('grapes')
    actual = fruits.find_from_end(1)
    assert 'pears' == actual