Why Probar?

Probar was created as a complete replacement for Playwright in the Jugar ecosystem.

The Problem with Playwright

1. JavaScript Dependency: Playwright requires Node.js and npm
2. Browser Overhead: Must download and run Chromium
3. Black Box Testing: Can only inspect DOM, not game state
4. CI Complexity: Requires browser installation in CI
5. Violates Zero-JS: Contradicts Jugar's core constraint

What Probar Solves

Zero JavaScript

Before (Playwright):
├── package.json
├── node_modules/
├── tests/
│   └── pong.spec.ts  ← TypeScript!
└── playwright.config.ts

After (Probar):
└── tests/
    └── probar_pong.rs  ← Pure Rust!

Direct State Access

Playwright treats the game as a black box:

// Can only check DOM
await expect(page.locator('#score')).toHaveText('10');

Probar can inspect game state directly:

#![allow(unused)]
fn main() {
// Direct access to game internals
let score = platform.get_game_state().score;
assert_eq!(score, 10);

// Check entity positions
for entity in platform.query_entities::<Ball>() {
    assert!(entity.position.y < 600.0);
}
}

Deterministic Testing

Playwright: Non-deterministic due to browser timing

// Flaky! Timing varies between runs
await page.waitForTimeout(100);
await expect(ball).toBeVisible();

Probar: Fully deterministic

#![allow(unused)]
fn main() {
// Exact frame control
for _ in 0..100 {
    platform.advance_frame(1.0 / 60.0);
}
let ball_pos = platform.get_ball_position();
assert_eq!(ball_pos, expected_pos);  // Always passes
}

Simpler CI

Playwright CI:

- name: Install Node.js
  uses: actions/setup-node@v3
- name: Install dependencies
  run: npm ci
- name: Install Playwright
  run: npx playwright install chromium
- name: Run tests
  run: npm test

Probar CI:

- name: Run tests
  run: cargo test

Feature Comparison

Migration Example

Before (Playwright)

import { test, expect } from '@playwright/test';

test('ball bounces off walls', async ({ page }) => {
  await page.goto('http://localhost:8080');

  // Wait for game to load
  await page.waitForSelector('#game-canvas');

  // Simulate gameplay
  await page.waitForTimeout(2000);

  // Check score changed (indirect verification)
  const score = await page.locator('#score').textContent();
  expect(parseInt(score)).toBeGreaterThan(0);
});

After (Probar)

#![allow(unused)]
fn main() {
#[test]
fn ball_bounces_off_walls() {
    let mut platform = WebPlatform::new_for_test(WebConfig::default());

    // Advance exactly 120 frames (2 seconds at 60fps)
    for _ in 0..120 {
        platform.advance_frame(1.0 / 60.0);
    }

    // Direct state verification
    let state = platform.get_game_state();
    assert!(state.ball_bounces > 0, "Ball should have bounced");
    assert!(state.score > 0, "Score should have increased");
}
}

Performance Comparison

When to Use Each

Use Probar for:

• Unit tests
• Integration tests
• Deterministic replay
• Fuzzing
• Performance benchmarks
• CI/CD pipelines

Use Browser Testing for:

• Visual regression (golden master)
• Cross-browser compatibility
• Real user interaction testing
• Production smoke tests