21

 import pytest

def power(x, y, expected):

    assert x ** y == expected

@pytest.mark.parametrize("x, y, expected", [

    (2, 2, 4),

    (2, 3, 8),

    (1, 9, 1),

    (0, 9, 0),

])

def test_power(x, y, expected):

    power(x, y, expected)