Chaos Testing Payment Failure Paths

Failure Scenario	Correct System Behavior	Bad Behavior to Avoid
Paystack API returns 500 on initialize	Return friendly error to user, log the raw error, allow retry	Expose raw "Internal Server Error" from Paystack to user
Webhook arrives but database is unavailable	Return 500 to Paystack (triggers retry), queue event for processing	Return 200 and silently drop the event
Same webhook delivered twice	First delivery fulfills; second is a no-op (idempotency)	Double fulfillment or duplicate order credit
Paystack verify call times out	Retry with exponential backoff (3 attempts), fail gracefully after	User sees payment failed even though Paystack succeeded
Webhook signature check fails (network glitch corrupted header)	Return 401, log the failure — do not process	Process the event anyway or crash with unhandled error

// Simulate Paystack API outage
describe('Paystack API 500 error', () => {
  it('returns friendly error when Paystack is down', async () => {
    global.fetch = jest.fn().mockResolvedValue({
      ok: false,
      status: 500,
      json: () => Promise.resolve({ status: false, message: 'Internal server error' }),
    });

    var res = await request(app).post('/api/checkout').send({ email: 'user@test.com', amount: 10000 });
    expect(res.status).toBe(503);
    expect(res.body.error).toBe('Payment service temporarily unavailable');
    // Should NOT expose: "Paystack: Internal server error"
  });
});

// Simulate DB failure during webhook
describe('Database failure during webhook', () => {
  it('returns 500 so Paystack retries', async () => {
    jest.spyOn(db.orders, 'update').mockRejectedValue(new Error('Connection refused'));

    var payload = { event: 'charge.success', data: { reference: 'ref_001', metadata: { order_id: 1 } } };
    var body = JSON.stringify(payload);
    var sig = crypto.createHmac('sha512', process.env.PAYSTACK_SECRET_KEY).update(body).digest('hex');

    var res = await request(app)
      .post('/webhook/paystack')
      .set('x-paystack-signature', sig)
      .send(body);

    // Must return 500 so Paystack retries — not 200
    expect(res.status).toBe(500);
  });
});

// Simulate duplicate webhook delivery
describe('Idempotency under duplicate delivery', () => {
  it('fulfills order exactly once for duplicate events', async () => {
    var fulfillSpy = jest.spyOn(orderService, 'fulfill');
    var payload = JSON.stringify({ event: 'charge.success', data: { reference: 'ref_dup', metadata: { order_id: 99 } } });
    var sig = crypto.createHmac('sha512', process.env.PAYSTACK_SECRET_KEY).update(payload).digest('hex');
    var headers = { 'x-paystack-signature': sig, 'Content-Type': 'application/json' };

    await request(app).post('/webhook/paystack').set(headers).send(payload).expect(200);
    await request(app).post('/webhook/paystack').set(headers).send(payload).expect(200);

    expect(fulfillSpy).toHaveBeenCalledTimes(1); // Not twice
  });
});

This guide is part of the Paystack testing guide.

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