The first request hits your API. A JWT is in play. You need to know: does authentication hold under real conditions? Integration testing with JWT-based authentication is the fastest way to be sure.
Unit tests catch syntax errors and simple logic bugs, but authentication lives in the real-world sequence of requests, headers, and tokens. Integration testing steps through that full sequence — login endpoints, token generation, token validation, and protected routes. It ensures your entire auth flow works exactly as intended, end to end.
With JWT-based authentication, each token carries claims about the user. Integration testing must verify that tokens are correctly signed, expire when expected, and reject unauthorized access. Test against scenarios such as expired tokens, forged tokens, missing claims, and invalid signatures. Simulate API calls with real JWTs, not mocks, to expose flaws before production.
A strong approach is to set up a dedicated test environment with the same configuration as production. Run automated tests that hit the actual auth endpoints. Verify status codes, payloads, and access control rules. Include concurrent requests and rate-limit checks to catch edge cases.