We will add some tests to check that the AI works properly. For a standard three by three game, the AI should never lose. That means when an AI plays against an AI, it should result in a draw. We can add a test for this. In lib/test/ai.ts, we import AVA and our own definitions.

import test from "ava"; 
import { createGrid, Grid, findWinner, isFull, getOptions, Player } from "../model"; 
import { minimax } from "../ai"; 
import { randomInt } from "../utils"; 

We create a function that simulates the whole gameplay.

type PlayerController = (grid: Grid) => Grid; 
function run(grid: Grid, a: PlayerController, b: PlayerController): Player { 
  const winner = findWinner(grid, 3); 
  if (winner !== Player.None) return winner; 
  if (isFull(grid)) return Player.None; 
  return run(a(grid), b, a); 
} 

We write a function that executes a step for the AI.

const aiPlayer = (player: Player) => (grid: Grid) =>
   minimax(grid...