CartFlow Pro — High-Traffic Flash Sale E-Commerce Platform

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

class CheckoutFlow {
  constructor(private page: Page) {}

  async addProductToCart(productId: string, quantity: number = 1) {
    await this.page.goto(`/products/${productId}`);
    await this.page.fill('[data-testid="quantity-input"]', quantity.toString());
    await this.page.click('[data-testid="add-to-cart-btn"]');
    
    // Wait for cart update
    await this.page.waitForLoadState('networkidle');
  }

  async proceedToCheckout() {
    await this.page.goto('/cart');
    await this.page.click('[data-testid="checkout-btn"]');
    
    // Verify checkout page loaded
    await expect(this.page.locator('[data-testid="payment-form"]')).toBeVisible();
  }

  async fillShippingInfo() {
    await this.page.fill('[data-testid="first-name"]', 'John');
    await this.page.fill('[data-testid="last-name"]', 'Doe');
    await this.page.fill('[data-testid="email"]', 'john@example.com');
    await this.page.fill('[data-testid="address"]', '123 Main St');
    await this.page.fill('[data-testid="city"]', 'New York');
    await this.page.fill('[data-testid="zip"]', '10001');
  }

  async fillPaymentInfo() {
    // Use Stripe test card
    const cardFrame = this.page.frameLocator('[data-testid="card-frame"]');
    await cardFrame.locator('[name="cardnumber"]').fill('4242424242424242');
    await cardFrame.locator('[name="exp-date"]').fill('12/25');
    await cardFrame.locator('[name="cvc"]').fill('123');
  }

  async completeCheckout() {
    await this.page.click('[data-testid="place-order-btn"]');
    
    // Wait for order confirmation
    await this.page.waitForURL('/order-confirmation/*');
    const orderId = new URL(this.page.url()).pathname.split('/').pop();
    
    return orderId;
  }
}

test('Complete checkout flow with valid payment', async ({ page }) => {
  const checkout = new CheckoutFlow(page);
  
  await checkout.addProductToCart('PROD-123', 2);
  await checkout.proceedToCheckout();
  await checkout.fillShippingInfo();
  await checkout.fillPaymentInfo();
  
  const orderId = await checkout.completeCheckout();
  
  expect(orderId).toBeTruthy();
  await expect(page.locator('[data-testid="order-total"]')).toContainText('$');
});

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

test('Race condition: 100 concurrent cart additions', async () => {
  const browser = await chromium.launch();
  const productId = 'PROD-LIMITED-STOCK';
  const numConcurrentUsers = 100;
  
  // Create 100 browser contexts simulating concurrent users
  const contexts = await Promise.all(
    Array(numConcurrentUsers).fill(null).map(() => browser.newContext())
  );
  
  // All users add same limited-stock product simultaneously
  const addCartPromises = contexts.map(async (context) => {
    const page = await context.newPage();
    await page.goto(`/products/${productId}`);
    
    const stockBefore = await page.locator('[data-testid="stock-count"]').textContent();
    
    await page.fill('[data-testid="quantity-input"]', '1');
    await page.click('[data-testid="add-to-cart-btn"]');
    
    // Wait for success message or error
    const successMsg = page.locator('[data-testid="item-added"]');
    const stockError = page.locator('[data-testid="out-of-stock"]');
    
    const result = await Promise.race([
      successMsg.waitFor({ state: 'visible' }),
      stockError.waitFor({ state: 'visible' })
    ]).then(() => 'success').catch(() => 'failed');
    
    await context.close();
    return { result, stockBefore };
  });
  
  const results = await Promise.all(addCartPromises);
  
  // Verify no double-sells occurred
  const successCount = results.filter(r => r.result === 'success').length;
  const stockLimit = parseInt(results[0].stockBefore);
  
  expect(successCount).toBeLessThanOrEqual(stockLimit);
  
  // Verify inventory is consistent
  const verifyPage = await browser.newPage();
  await verifyPage.goto(`/products/${productId}`);
  const finalStock = parseInt(await verifyPage.locator('[data-testid="stock-count"]').textContent());
  
  expect(finalStock).toBe(stockLimit - successCount);
  
  await browser.close();
});