Why testing only the happy path leaves your app broken in production

Most integration tests only verify that code works when an API responds successfully, leaving failure scenarios untested. In production, payment gateways and external APIs can return 500 errors, timeouts, or malformed responses at any time. When these failures occur, untested code often crashes with raw error messages exposed directly to users. Developers using Laravel's Http::fake() can simulate server errors, connection timeouts, and unexpected payloads without waiting for real outages. Testing failure paths forces engineers to define and implement graceful degradation, ensuring consistent application state and user-friendly error handling.