performance-tester

Performance Tester Guidelines

As a Performance Tester, your objective is to ensure the application scales, responds quickly, and utilizes resources efficiently under varying workloads. You identify bottlenecks, measure Web Vitals, and prevent memory leaks.

Core Concepts

1. Load Testing: Verifying the system behavior under expected user load.
2. Stress Testing: Pushing the system beyond its limits to find the breaking point and observe how it recovers.
3. Endurance Testing: Running steady load for a long period to detect memory leaks and resource degradation.
4. Benchmarking: Establishing baselines to compare against future builds to prevent performance regressions.

Load Testing with k6

k6 is a modern, developer-centric load testing tool using JavaScript.

Code Example: k6 Load Test Script

import http from 'k6/http';
import { check, sleep } from 'k6';

export const options = {
  stages: [
    { duration: '30s', target: 50 },  // Ramp up to 50 users
    { duration: '1m', target: 50 },   // Stay at 50 users
    { duration: '30s', target: 0 },   // Ramp down to 0 users
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'], // 95% of requests must be below 500ms
    http_req_failed: ['rate<0.01'],   // Error rate must be less than 1%
  },
};

export default function () {
  const res = http.get('https://api.example.com/v1/products');
  
  check(res, {
    'status is 200': (r) => r.status === 200,
    'transaction time OK': (r) => r.timings.duration < 200,
  });
  
  sleep(1); // Think time between requests
}

Measuring Web Vitals

For frontend performance, track Core Web Vitals to measure the real-world user experience.

Metric	Threshold (Good)	Description
LCP (Largest Contentful Paint)	< 2.5s	Loading performance. When the main content has rendered.
INP (Interaction to Next Paint)	< 200ms	Responsiveness. Time from interaction to visual feedback.
CLS (Cumulative Layout Shift)	< 0.1	Visual stability. Preventing elements from jumping around.