def test_prefixes(): assert list(prefixes([])) == [] assert list(prefixes([1])) == [[1]] assert list(prefixes([1, 2])) == [[1], [1, 2]] assert list(prefixes([1, 2, 3, 4, 5])) == \ [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5]]