Performance Testing — Explained with Examples

Performance testing evaluates how a system behaves under various load conditions, measuring speed, responsiveness, and stability to identify bottlenecks.

Performance testing ensures your application meets speed and stability requirements. It answers questions like: “How many users can this handle?” and “What happens when traffic spikes?”

Types of Performance Testing

Load Testing — simulates expected user traffic to measure response times and throughput under normal conditions.

Stress Testing — pushes beyond normal capacity to find the breaking point.

Spike Testing — sudden, dramatic increases in load to test recovery behavior.

Endurance Testing — sustained load over hours or days to detect memory leaks or degradation.

Example: k6 Load Test

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

export const options = {
  stages: [
    { duration: '2m', target: 100 },  // Ramp up to 100 users
    { duration: '5m', target: 100 },  // Stay at 100 for 5 minutes
    { duration: '2m', target: 200 },  // Ramp to 200
    { duration: '5m', target: 200 },  // Stay at 200
    { duration: '2m', target: 0 },    // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'], // 95% of requests under 500ms
    http_req_failed: ['rate<0.01'],   // Less than 1% errors
  },
};

export default function () {
  const res = http.get('https://api.example.com/users');
  check(res, {
    'status is 200': (r) => r.status === 200,
    'response time < 300ms': (r) => r.timings.duration < 300,
  });
  sleep(1);
}

// k6 output
http_req_duration......: avg=245ms  min=120ms  med=230ms  max=890ms
http_req_failed........: 0.3%  ✓ 743821    ✗ 2219
vus....................: 200    min=0     max=200

Real-World Analogy

Performance testing is like stress-testing a bridge. You start with a few pedestrians (10 users), then cars (100), then trucks (1000). You check: does the bridge sway more than expected? Do cracks appear? What happens when a convoy of trucks stops in the middle (spike)? How does the bridge hold up after months of continuous traffic (endurance)?

Key Metrics

Related Terms

Load Balancing, Observability, Rate Limiting, Scalability, API Gateway