@Test
public void testForwardOtherSignal() {

    new TestKit(actorSystem) {{
        final Signal<?> signal = Mockito.mock(Signal.class);
        Mockito.when(signal.getDittoHeaders()).thenReturn(DittoHeaders.empty());
        final Props props = ConnectivityProxyActor.props(getRef());
        final ActorRef proxy = actorSystem.actorOf(props);
        // WHEN: signal is sent to proxy actor
        proxy.tell(signal, getRef());
        // THEN: signal is forwarded to concierge
        expectMsg(signal);
        // WHEN: concierge responds
        final Signal<?> response = Mockito.mock(Signal.class);
        Mockito.when(response.getDittoHeaders()).thenReturn(DittoHeaders.empty());
        getLastSender().tell(response, ActorRef.noSender());
        // THEN: original sender receives response
        expectMsg(response);
    }};
}