Verified comprehensive test infrastructure already exists in proxy/helpers_test.go:
- MockUpstream with configurable scenarios
- Test mode configuration (TestModeEnv, TestMaxRetriesEnv)
- Request builders and response assertions
- Proxy handler factory and execution helpers
- All helper tests pass successfully
No code changes needed - infrastructure is complete and functional.
Co-Authored-By: Claude <noreply@anthropic.com>
