Explain common HTTP Status Codes used in API Testing

HTTP Status Codes are three-digit numbers returned by servers to indicate the result of an HTTP request.

2xx - Success

• 200 OK: Request successful (GET, PUT, PATCH)
• 201 Created: Resource created successfully (POST)
• 204 No Content: Success but no content to return (DELETE)

4xx - Client Errors

• 400 Bad Request: Invalid request syntax
• 401 Unauthorized: Authentication required
• 403 Forbidden: Server refuses to authorize
• 404 Not Found: Resource doesn’t exist
• 405 Method Not Allowed: HTTP method not supported
• 409 Conflict: Request conflicts with current state
• 422 Unprocessable Entity: Validation errors
• 429 Too Many Requests: Rate limit exceeded

5xx - Server Errors

• 500 Internal Server Error: Generic server error
• 502 Bad Gateway: Invalid response from upstream server
• 503 Service Unavailable: Server temporarily unavailable
• 504 Gateway Timeout: Upstream server timeout

Testing Scenarios

• Verify correct status code for each operation
• Test error handling (4xx, 5xx responses)
• Validate response body matches status code
• Check status codes for edge cases