Third-Party API Simulation

Your app integrates with payment gateways, email services, and third-party APIs. Testing against real services means rate limits, costs, and polluted test data. MockStation lets you simulate these services locally and in CI.

The Third-Party Problem

Real third-party APIs come with constraints:

Rate limits: Hit limits during development, get blocked
Costs: Payment API calls cost money, even in test mode
Test data pollution: Real services accumulate test records
Sandbox limitations: Test environments don't support all scenarios
Network dependency: External service downtime blocks your work

Common Third-Party APIs to Mock

Payment Gateways

Stripe, PayPal, Braintree, Square

Email Services

SendGrid, Mailgun, AWS SES, Postmark

Cloud Services

AWS, GCP, Azure APIs

Auth Providers

OAuth, Auth0, Firebase Auth

Example: Mock Stripe API

Create Charge

POST/v1/charges

{
  "id": "ch_{{$randomUUID}}",
  "object": "charge",
  "amount": "{{request.body.amount}}",
  "currency": "{{request.body.currency}}",
  "status": "succeeded",
  "paid": true,
  "captured": true,
  "payment_method": "pm_{{$randomUUID}}",
  "receipt_url": "https://pay.stripe.com/receipts/{{$randomUUID}}",
  "created": {{$timestamp}}
}

Card Declined Scenario

POST/v1/charges/declinedStatus: 402

{
  "error": {
    "type": "card_error",
    "code": "card_declined",
    "message": "Your card was declined.",
    "decline_code": "insufficient_funds"
  }
}

Example: Mock SendGrid API

Send Email

POST/v3/mail/sendStatus: 202

{
  "message_id": "{{$randomUUID}}",
  "status": "accepted"
}

Example: Mock OAuth Provider

Token Exchange

POST/oauth/token

{
  "access_token": "{{$randomUUID}}-{{$randomUUID}}",
  "token_type": "Bearer",
  "expires_in": 3600,
  "refresh_token": "{{$randomUUID}}",
  "scope": "read write"
}

User Info

GET/oauth/userinfo

{
  "sub": "{{$randomUUID}}",
  "email": "{{$faker.internet.email}}",
  "email_verified": true,
  "name": "{{$faker.person.fullName}}",
  "picture": "{{$faker.image.avatar}}",
  "locale": "en-US"
}

Configuration Pattern

Use environment variables to switch between mock and real APIs:

config/services.ts

const config = {
  stripe: {
    development: 'https://api.mockstation.io/v1/my-app/stripe',
    test: 'https://api.mockstation.io/v1/my-app/stripe',
    production: 'https://api.stripe.com',
  },
  sendgrid: {
    development: 'https://api.mockstation.io/v1/my-app/sendgrid',
    test: 'https://api.mockstation.io/v1/my-app/sendgrid',
    production: 'https://api.sendgrid.com',
  },
};

const env = process.env.NODE_ENV || 'development';
export const STRIPE_API_URL = config.stripe[env];
export const SENDGRID_API_URL = config.sendgrid[env];

Benefits

Zero costs: No charges for payment API calls
No rate limits: Test as much as you want
Clean data: No test pollution in real services
Test all scenarios: Declined cards, bounced emails, auth failures
Offline capable: External service outages don't block you
Fast: Mock responses in milliseconds

Get Started

Mock your third-party integrations:

Create a free account
Create endpoints matching the third-party API structure
Add both success and error scenarios
Point your app to mock URLs in development
Test freely without costs or limits