Testing API Failure Scenarios: Why Success Paths Aren't Enough

Developers often verify only the successful 200 OK response, but production systems regularly face server errors, missing data, and network problems. The article illustrates how a simple frontend fetch can crash or leave users stranded when responses are unexpected. It recommends deliberately testing cases such as 500 errors, absent JSON fields, expired sessions, interrupted connections, and requests sent to the wrong environment. Mocking API responses lets teams simulate these conditions without relying on a live backend. Network interception tools such as Proxyceptor are presented as another option for modifying requests and responses without changing application code.