@Test
public void shouldRespondToObservationRequest_errorResponse() {

    Callback<CoapPacket> respCallback = mock(Callback.class);
    server.observe("/test", LOCAL_5683, respCallback, "aa".getBytes(), TransportContext.NULL);
    verifyMakeRequest_andThen().call(newCoapPacket().ack(Code.C404_NOT_FOUND).build());
    verify(respCallback).callException(isA(ObservationNotEstablishedException.class));
}