An illustrative snippet for the blog post

sample_test.py

import pytest

@pytest.mark.parametrize('state', [
    'ooo|x.x|..x',
    'xo.|xo.|x..',
    'x..|.xo|o.x'
])
def test_game_has_winner(state):
    game = Game(state)
    assert game.has_winner()

class Game:
    def __init__(self, state):
        self.state = state_from_string(state)

    def has_winner(self):
        pass  # check rows, columns, and diagonals

def state_from_string(line):
    return [list(row) for row in line.split('|')]