Simulation & testing

Elarion.Connections.Simulation ships the pieces every gateway test suite — and every runnable dev/demo device simulator — otherwise hand-rolls. SimulatedClientConnection is an in-memory sink double — register it with the real registry and drive twins, observers, and presence logic deterministically: await its Sent channel for outbound messages, answer InvokeAsync via InvokeResponder, and Close() it to assert your code survives ClientConnectionClosedException. AwaitableConnectionObserver turns lifecycle edges into awaitable completions (with Reset() for reconnect scenarios). TcpSimulatorClient is the framed client for simulated devices/peers: connect it to a listener (or wrap the accepted side of a fake device an Elarion dialer reached) and speak whole messages through the endpoint's own framer, with text helpers for challenge/response handshakes.

The default for codec/handler-level work is fully in-memory — no OS sockets, ports, or firewall prompts: InMemoryTcpLink.Start(handler, registry, o => o.Framer = …) runs the complete connection lifecycle (per-connection sessions, handshake, framing, registry, codec, idle hook) over an in-memory duplex pair, hands you the simulator-side Client, a deterministic ServerConnection await (the registered sink — no polling, no handshake races), and a ServerCompletion for teardown assertions. By default the client speaks the endpoint framer instance (fine for stateless framers); when the handler's sessions create a stateful framer (negotiated framing, encryption toggles), pass the client its own instance via the clientFramer parameter — the two ends of a real link never share framing state. Reserve real sockets (loopback TCP, Kestrel + ClientWebSocket) for integration tests of the adapters themselves — the separate Elarion.Connections.AspNetCore.Simulation package's WebSocketTestHost covers a real Kestrel upgrade, handshake, codec, and close path. InMemoryDuplexStream.CreatePair() is public for anything else that wants a socket pair without the socket.