Simulating API Failures
Test your application's resilience by simulating various API failure scenarios. This guide shows you how to create realistic error conditions to ensure your app handles failures gracefully.
Creating Error Responses
Define custom error responses with specific status codes, messages, and response bodies to test how your frontend application handles different failure scenarios.
400 Bad Request
Invalid parameters or malformed request
401 Unauthorized
Missing or invalid authentication
404 Not Found
Resource does not exist
500 Server Error
Unexpected error on server
Configuring Failure Scenarios
Create complex failure scenarios like network timeouts, rate limiting, and partial data failures. Simulate intermittent issues to test retry logic and error recovery mechanisms.
Common Failure Types
Network timeouts and latency
Rate limiting with Retry-After headers
Malformed responses with partial data
Authentication failures with token expiration
Intermittent failures that occur randomly
Rate Limit Error Configuration
{
"status": 429,
"statusText": "Too Many Requests",
"body": {
"error": "rate_limit_exceeded",
"message": "API rate limit exceeded",
"retry_after": 30
},
"headers": {
"Retry-After": "30",
"X-RateLimit-Limit": "100",
"X-RateLimit-Remaining": "0"
},
"delay": 1500
}Editing & Expanding Endpoints
Modify existing endpoints to include failure cases or expand them with additional error handling logic. Evolve your test scenarios as your application develops.
Conditional Failures
Create sophisticated failure responses that only occur under specific conditions based on request parameters, headers, or body content.
Conditional Failure Logic
// Fail if request includes certain parameters
if (request.body && request.body.userId === "invalid") {
return {
status: 400,
body: {
error: "invalid_user",
message: "The specified user ID is invalid"
}
};
}
// Fail if authorization header is missing or malformed
if (!request.headers.authorization ||
!request.headers.authorization.startsWith("Bearer ")) {
return {
status: 401,
body: {
error: "unauthorized",
message: "Valid authorization token required"
}
};
}
// Otherwise return success
return {
status: 200,
body: {
success: true,
data: { /* normal response data */ }
}
};Testing Tips
- •Test how your UI displays different error messages to users
- •Verify that your application's retry logic respects Retry-After headers
- •Check that authentication failures properly redirect to login screens
- •Ensure loading states and error states display correctly during timeouts
Testing Failure Responses
Test your configured failure scenarios using Postman or your application to verify that error handling works correctly.
Monitoring Error Responses
Track all simulated failures with comprehensive logging of status codes, response times, and error details to help with debugging.
Key Benefits
By thoroughly testing how your application responds to API failures, you can build more robust software that gracefully handles unexpected conditions.
Resilient Applications
Ensure your app gracefully handles API failures and maintains a good user experience
Comprehensive Testing
Test complex edge cases and verify error handling before deploying to production
Better User Experience
Provide helpful error messages and recovery options instead of generic failure screens