k6 Load Testing with JavaScript

// ══════════════════════════════════════════════════════════════
// INSTALL: brew install k6 (macOS) / choco install k6 (Windows)
// RUN:     k6 run load_test.js
// ══════════════════════════════════════════════════════════════

import http from 'k6/http';
import { check, sleep, group } from 'k6';
import { Counter, Rate, Trend } from 'k6/metrics';

// ── CUSTOM METRICS ────────────────────────────────────────────
const loginErrors = new Counter('login_errors');
const checkoutDuration = new Trend('checkout_duration');
const errorRate = new Rate('error_rate');

// ── TEST OPTIONS (load profile) ───────────────────────────────
export const options = {
  stages: [
    { duration: '2m',  target: 50  },  // Ramp up to 50 users over 2 min
    { duration: '5m',  target: 50  },  // Hold at 50 users for 5 min
    { duration: '2m',  target: 100 },  // Ramp up to 100 users
    { duration: '10m', target: 100 },  // Hold at 100 users for 10 min
    { duration: '2m',  target: 0   },  // Ramp down to 0
  ],
  
  // ── THRESHOLDS (define pass/fail criteria) ────────────────
  thresholds: {
    http_req_duration: [
      'p(95)<500',    // 95% of requests complete in <500ms
      'p(99)<1000',   // 99% complete in <1000ms
    ],
    http_req_failed: ['rate<0.01'],  // Error rate below 1%
    error_rate: ['rate<0.05'],       // Custom error rate below 5%
    checkout_duration: ['p(95)<2000'], // Checkout under 2s at p95
  },
};

// ── SETUP (runs once before the test) ─────────────────────────
export function setup() {
  // Create test data (e.g., seed products in test DB via API)
  const res = http.post('https://staging.myapp.com/api/test/seed', JSON.stringify({
    products: 100, users: 50
  }), { headers: { 'Content-Type': 'application/json' } });
  return { products: res.json().productIds };  // Returned data available in default()
}

// ── MAIN FUNCTION (each virtual user runs this in a loop) ──────
export default function(data) {
  const BASE_URL = 'https://staging.myapp.com';

  group('Authentication', () => {
    const loginRes = http.post(`${BASE_URL}/api/auth/login`, JSON.stringify({
      email: `user${__VU}@test.com`,  // __VU = virtual user number (unique per user)
      password: 'Test@1234'
    }), { headers: { 'Content-Type': 'application/json' } });
    
    const loginOk = check(loginRes, {
      'login status is 200': (r) => r.status === 200,
      'login returns token': (r) => r.json().token !== undefined,
      'login time < 500ms': (r) => r.timings.duration < 500,
    });
    
    if (!loginOk) { loginErrors.add(1); errorRate.add(1); return; }
    
    const token = loginRes.json().token;
    const authHeaders = { headers: { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' } };
    
    sleep(1);  // Think time: 1 second
  });

  group('Product Browsing', () => {
    const productId = data.products[Math.floor(Math.random() * data.products.length)];
    const productRes = http.get(`${BASE_URL}/api/products/${productId}`, authHeaders);
    
    check(productRes, {
      'product page loads': (r) => r.status === 200,
      'product has price': (r) => r.json().price > 0,
    });
    
    sleep(__ENV.THINK_TIME || 2);  // Configurable think time via env var
  });
}

// ── TEARDOWN (runs once after the test) ───────────────────────
export function teardown(data) {
  // Clean up test data
  http.del('https://staging.myapp.com/api/test/cleanup');
}

// ── RUN WITH OPTIONS ──────────────────────────────────────────
// k6 run load_test.js                          # Default
// k6 run --env THINK_TIME=3 load_test.js       # Override think time
// k6 run --out json=results.json load_test.js  # Export raw metrics
// k6 run --out influxdb=http://localhost:8086 load_test.js  # Grafana dashboard