Testing Workflow

# Unit / integration
npx vitest run --coverage          # all tests + coverage
npx vitest run src/utils.test.ts   # single file

# E2E (Playwright)
npx playwright test                # all E2E suites
npx playwright test --ui           # interactive mode

// Unit test with mock
import { describe, it, expect, vi } from 'vitest';
import { fetchItems } from './api';

describe('fetchItems', () => {
  it('returns filtered results', async () => {
    vi.spyOn(global, 'fetch').mockResolvedValue(
      new Response(JSON.stringify([{ id: 1, name: 'test' }]))
    );
    const items = await fetchItems({ category: 'active' });
    expect(items).toHaveLength(1);
    expect(fetch).toHaveBeenCalledWith(expect.stringContaining('category=active'));
  });
});

// E2E test (Playwright)
import { test, expect } from '@playwright/test';

test('filter updates results and URL', async ({ page }) => {
  await page.goto('/items');
  await page.getByRole('combobox', { name: 'Category' }).selectOption('active');
  await expect(page).toHaveURL(/category=active/);
  await expect(page.getByRole('listitem')).not.toHaveCount(0);
});