callback global sinon crash

AutomForArduino.cpp

@@ -118,7 +118,11 @@ public:
   }
 };
 
+callback cb;
+
 void mqtt_open(mqtt::async_client* client) {
+
+  client->set_callback(cb);
   mqtt::connect_options connOpts;
   connOpts.set_clean_session(true);
   connOpts.set_user_name("admin");