Fake HA server (aiohttp.web) simulates full API surface over real TCP: - WebSocket auth handshake + event push - REST endpoints (states, services, notifications) 14 integration tests verify end-to-end flows without mocks: - WS connect/auth/subscribe/event-forwarding/disconnect - REST list/get/call-service against fake server - send() notification delivery and auth failure - 401/500 error handling