Load Testing a Payment Endpoint Responsibly

Your payment flow has two external dependencies: the Paystack API and your database. Load tests should measure your system, not stress Paystack's infrastructure.

For checkout initiation load tests:

1. Add a test mode flag in your checkout endpoint that returns a mocked authorization_url without calling Paystack
2. Or use a feature flag that swaps the Paystack client for a stub that returns fixed responses
3. Run k6 or Artillery against this endpoint — you are testing your server's throughput, DB connection pooling, and response time

For webhook handler load tests:

1. Pre-generate 10,000 valid HMAC-signed webhook payloads (charge.success events)
2. Send them concurrently to your webhook endpoint
3. Measure DB write throughput, connection pool, and queue depth

// load-tests/checkout.js
// Run: k6 run load-tests/checkout.js
import http from 'k6/http';
import { check, sleep } from 'k6';
import { Rate } from 'k6/metrics';

var errorRate = new Rate('errors');

export var options = {
  stages: [
    { duration: '30s', target: 10 },  // Ramp up to 10 concurrent users
    { duration: '60s', target: 50 },  // Ramp up to 50 concurrent users
    { duration: '30s', target: 0 },   // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(99)<500'], // 99% of requests under 500ms
    errors: ['rate<0.01'],            // Less than 1% error rate
  },
};

export default function () {
  var payload = JSON.stringify({
    email: 'loadtest+' + __VU + '@example.com',
    amount: 10000,
    order_id: Math.floor(Math.random() * 1000000),
  });

  var res = http.post('https://staging.yourapp.com/api/checkout', payload, {
    headers: {
      'Content-Type': 'application/json',
      // Include auth if needed
    },
  });

  check(res, {
    'status is 200': (r) => r.status === 200,
    'has authorization_url': (r) => r.json('authorization_url') !== undefined,
  });

  errorRate.add(res.status !== 200);
  sleep(1);
}

Ensure your staging checkout endpoint is configured to mock the Paystack API call during load tests (use PAYSTACK_MOCK=true environment variable).

This guide is part of the Paystack testing guide.

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