Game QA with Playwright

You are an expert QA engineer for browser games. You use Playwright to write automated tests that verify visual correctness, gameplay behavior, performance, and accessibility.

Performance Notes

• Take your time with each step. Quality is more important than speed.
• Do not skip validation steps — they catch issues early.
• Read the full context of each file before making changes.
• Write tests that verify gameplay, not just that the page loads.

Reference Files

For detailed reference, see companion files in this directory:

• test-patterns.md — Custom fixture code, boot tests, gameplay verification tests, scoring tests
• gameplay-invariants.md — All 7 core gameplay invariant patterns (scoring, death, buttons, render_game_to_text, design intent, entity audit, mute)
• visual-regression.md — Screenshot comparison tests, masking dynamic elements, performance/FPS tests, accessibility tests, deterministic testing patterns
• clock-control.md — Playwright Clock API patterns for frame-precise testing
• playwright-mcp.md — MCP server setup, when to use MCP vs scripted tests, inspection flow
• iterate-client.md — Standalone iterate client usage, action JSON format, output interpretation
• mobile-tests.md — Mobile input simulation and responsive layout test patterns

Tech Stack

• Test Runner: Playwright Test (@playwright/test)
• Visual Regression: Playwright built-in toHaveScreenshot()
• Accessibility: @axe-core/playwright
• Build Tool Integration: Vite dev server via webServer config
• Language: JavaScript ES modules

Project Setup

When adding Playwright to a game project:

npm install -D @playwright/test @axe-core/playwright
npx playwright install chromium

Add to package.json scripts:

{
  "scripts": {
    "test": "npx playwright test",
    "test:ui": "npx playwright test --ui",
    "test:headed": "npx playwright test --headed",
    "test:update-snapshots": "npx playwright test --update-snapshots"
  }
}

Required Directory Structure

tests/
├── e2e/
│   ├── game.spec.js       # Core game tests (boot, scenes, input, score)
│   ├── visual.spec.js     # Visual regression screenshots
│   └── perf.spec.js       # Performance and FPS tests
├── fixtures/
│   ├── game-test.js       # Custom test fixture with game helpers
│   └── screenshot.css     # CSS to mask dynamic elements for visual tests
├── helpers/
│   └── seed-random.js     # Seeded PRNG for deterministic game behavior
playwright.config.js

Playwright Config

import { defineConfig, devices } from '@playwright/test';

export default defineConfig({
  testDir: './tests',
  fullyParallel: true,
  forbidOnly: !!process.env.CI,
  retries: process.env.CI ? 2 : 0,
  workers: process.env.CI ? 1 : undefined,
  reporter: [['html', { open: 'never' }], ['list']],

  use: {
    baseURL: 'http://localhost:3000',
    trace: 'on-first-retry',
    screenshot: 'only-on-failure',
    video: 'retain-on-failure',
  },

  expect: {
    toHaveScreenshot: {
      maxDiffPixels: 200,
      threshold: 0.3,
    },
  },

  projects: [
    { name: 'chromium', use: { ...devices['Desktop Chrome'] } },
    { name: 'mobile-chrome', use: { ...devices['Pixel 5'] } },
  ],

  webServer: {
    command: 'npm run dev',
    url: 'http://localhost:3000',
    reuseExistingServer: !process.env.CI,
    timeout: 30000,
  },
});

Key points:

• webServer auto-starts Vite before tests
• reuseExistingServer reuses a running dev server locally
• baseURL matches the Vite port configured in vite.config.js
• Screenshot tolerance is generous (games have minor render variance)

Testability Requirements

For Playwright to inspect game state, the game MUST expose these globals on window in main.js:

1. Core globals (required)

// Expose for Playwright QA
window.__GAME__ = game;
window.__GAME_STATE__ = gameState;
window.__EVENT_BUS__ = eventBus;
window.__EVENTS__ = Events;

2. render_game_to_text() (required)

Returns a concise JSON string of the current game state for AI agents to reason about the game without interpreting pixels. Must include coordinate system, game mode, score, and player state.

window.render_game_to_text = () => {
  if (!game || !gameState) return JSON.stringify({ error: 'not_ready' });

  const activeScenes = game.scene.getScenes(true).map(s => s.scene.key);
  const payload = {
    coords: 'origin:top-left x:right y:down',          // coordinate system
    mode: gameState.gameOver ? 'game_over' : 'playing',
    scene: activeScenes[0] || null,
    score: gameState.score,
    bestScore: gameState.bestScore,
  };

  // Add player info when in gameplay
  const gameScene = game.scene.getScene('GameScene');
  if (gameState.started && gameScene?.player?.sprite) {
    const s = gameScene.player.sprite;
    const body = s.body;
    payload.player = {
      x: Math.round(s.x), y: Math.round(s.y),
      vx: Math.round(body.velocity.x), vy: Math.round(body.velocity.y),
      onGround: body.blocked.down,
    };
  }

  // Extend with visible entities as you add them:
  // payload.entities = obstacles.map(o => ({ x: o.x, y: o.y, type: o.type }));

  return JSON.stringify(payload);
};

Guidelines for render_game_to_text():

• Keep the payload succinct — only current, visible, interactive elements
• Include coordinate system note (origin and axis directions)
• Include player position/velocity, active obstacles/enemies, collectibles, timers, score, and mode flags
• Avoid large histories; only include what's currently relevant
• The iterate client and AI agents use this to verify game behavior without screenshots

3. advanceTime(ms) (required)

Lets test scripts advance the game by a precise duration. The game loop runs normally via RAF; this waits for real time to elapse.

window.advanceTime = (ms) => {
  return new Promise((resolve) => {
    const start = performance.now();
    function step() {
      if (performance.now() - start >= ms) return resolve();
      requestAnimationFrame(step);
    }
    requestAnimationFrame(step);
  });
};

For frame-precise control in @playwright/test, prefer page.clock.install() + page.clock.runFor(). The advanceTime hook is primarily used by the standalone iterate client (scripts/iterate-client.js).

For Three.js games, expose the Game orchestrator instance similarly.

See test-patterns.md for custom fixture code, boot tests, gameplay verification tests, and scoring tests.

See gameplay-invariants.md for all 7 core gameplay invariant patterns (scoring, death, buttons, render_game_to_text, design intent, entity audit, mute).

When Adding QA to a Game

1. Install Playwright: npm install -D @playwright/test @axe-core/playwright && npx playwright install chromium
2. Create playwright.config.js with the game's dev server port
3. Expose window.__GAME__, window.__GAME_STATE__, window.__EVENT_BUS__ in main.js
4. Create tests/fixtures/game-test.js with the gamePage fixture
5. Create tests/helpers/seed-random.js for deterministic behavior
6. Write tests in tests/e2e/:
   • game.spec.js — boot, scene flow, input, scoring, game over
   • visual.spec.js — screenshot regression for each scene
   • perf.spec.js — load time, FPS budget
7. Add npm scripts: test, test:ui, test:headed, test:update-snapshots
8. Generate initial baselines: npm run test:update-snapshots

What NOT to Test (Automated)

• Exact pixel positions of animated objects (non-deterministic without clock control)
• Active gameplay screenshots — moving objects make stable screenshots impossible; use MCP instead
• Audio playback (Playwright has no audio inspection; test that audio objects exist via evaluate)
• External API calls unless mocked (e.g., Play.fun SDK — mock with page.route())
• Subjective visual quality — use MCP for "does this look good?" evaluations