fool-cardgame/tests/core/match/soak.spec.ts

import { describe, expect, it } from 'vitest';
import { BasicBot } from '@core/bot/BasicBot';
import { Match } from '@core/match/Match';
import { runMatch } from '@core/match/runMatch';
import { legalActions } from '@core/rules/DurakRules';
import { PlayerId } from '@core/rules/GameState';
import { Rng } from '@core/util/Rng';
import { assertInvariants } from '../../support/invariants';

/** Plays one seeded match, checking every reachable state along the way. */
function playChecked(players: PlayerId[], seed: number, pick?: (n: number, rng: Rng) => number) {
    const match = new Match({ players, seed });
    const bots = Object.fromEntries(players.map((p) => [p, new BasicBot(p)]));
    const rng = new Rng(seed ^ 0x5f3759df);

    assertInvariants(match.state);

    let actions = 0;
    while (!match.finished) {
        const actor = match.currentActor;
        expect(actor).not.toBeNull();

        const options = legalActions(match.state, actor as PlayerId);
        expect(options.length).toBeGreaterThan(0);

        const action = pick
            ? options[pick(options.length, rng)]
            : bots[actor as PlayerId].decide(match.viewFor(actor as PlayerId));

        match.perform(action);
        assertInvariants(match.state);

        if (++actions > 4000) {
            throw new Error(`Match ${seed} will not end`);
        }
    }

    return { match, actions };
}

describe('soak: two basic bots', () => {
    it('finishes 2000 seeded matches with every invariant intact', () => {
        const outcomes = new Map<string, number>();

        for (let seed = 0; seed < 2000; seed++) {
            const { match } = playChecked(['you', 'bot'], seed);
            const key = match.loser ?? 'draw';
            outcomes.set(key, (outcomes.get(key) ?? 0) + 1);
        }

        // Every match must have produced a verdict.
        const total = [...outcomes.values()].reduce((a, b) => a + b, 0);
        expect(total).toBe(2000);

        // Two identical bots: neither seat should be losing almost every game.
        // A wide band — this is a smoke check on the rules, not a balance claim.
        for (const seat of ['you', 'bot']) {
            expect(outcomes.get(seat) ?? 0).toBeGreaterThan(2000 * 0.2);
        }
    });

    it('finishes three-player matches too', () => {
        for (let seed = 0; seed < 300; seed++) {
            const { match } = playChecked(['a', 'b', 'c'], seed);
            expect(match.finished).toBe(true);
            if (match.loser !== null) {
                expect(['a', 'b', 'c']).toContain(match.loser);
            }
        }
    });
});

describe('soak: random legal play', () => {
    it('survives 1000 matches of arbitrary legal moves', () => {
        for (let seed = 0; seed < 1000; seed++) {
            const { match } = playChecked(['you', 'bot'], seed, (n, rng) => rng.nextInt(n));
            expect(match.finished).toBe(true);
        }
    });

    it('survives random play at a crowded table', () => {
        for (let seed = 0; seed < 200; seed++) {
            const { match } = playChecked(['a', 'b', 'c', 'd'], seed, (n, rng) => rng.nextInt(n));
            expect(match.finished).toBe(true);
        }
    });
});

describe('match determinism', () => {
    it('replays a seed move for move', () => {
        const first: string[] = [];
        const second: string[] = [];

        for (const trace of [first, second]) {
            const match = new Match({ players: ['you', 'bot'], seed: 31337 });
            runMatch(match, { you: new BasicBot('you'), bot: new BasicBot('bot') }, { trace });
        }

        expect(first).toEqual(second);
        expect(first.length).toBeGreaterThan(10);
    });

    it('reports the same loser for the same seed', () => {
        const play = () => {
            const match = new Match({ players: ['you', 'bot'], seed: 555 });
            return runMatch(match, { you: new BasicBot('you'), bot: new BasicBot('bot') });
        };
        expect(play()).toEqual(play());
    });
});

describe('runMatch', () => {
    it('stops at a seat it has no bot for', () => {
        const match = new Match({ players: ['you', 'bot'], seed: 8 });
        const result = runMatch(match, { bot: new BasicBot('bot') });

        expect(match.finished).toBe(false);
        expect(match.currentActor).toBe('you');
        expect(result.loser).toBeNull();
    });

    it('refuses to loop forever', () => {
        const match = new Match({ players: ['you', 'bot'], seed: 8 });
        expect(() => runMatch(
            match,
            { you: new BasicBot('you'), bot: new BasicBot('bot') },
            { maxActions: 3 },
        )).toThrow(/did not finish/);
    });
});