Add unit tests for MQTT (#5724)

* Add unit tests for MQTT

* Test received fields

src/mesh/MeshService.h

@@ -142,7 +142,7 @@ class MeshService
     void sendToPhone(meshtastic_MeshPacket *p);
 
     /// Send an MQTT message to the phone for client proxying
-    void sendMqttMessageToClientProxy(meshtastic_MqttClientProxyMessage *m);
+    virtual void sendMqttMessageToClientProxy(meshtastic_MqttClientProxyMessage *m);
 
     /// Send a ClientNotification to the phone
     void sendClientNotification(meshtastic_ClientNotification *cn);

src/mesh/NodeDB.h

@@ -145,7 +145,7 @@ class NodeDB
         return &meshNodes->at(x);
     }
 
-    meshtastic_NodeInfoLite *getMeshNode(NodeNum n);
+    virtual meshtastic_NodeInfoLite *getMeshNode(NodeNum n);
     size_t getNumMeshNodes() { return numMeshNodes; }
 
     // returns true if the maximum number of nodes is reached or we are running low on memory

src/mesh/RadioLibInterface.cpp

@@ -431,6 +431,7 @@ void RadioLibInterface::handleReceiveInterrupt()
             // nodes.
             meshtastic_MeshPacket *mp = packetPool.allocZeroed();
 
+            // Keep the assigned fields in sync with src/mqtt/MQTT.cpp:onReceiveProto
             mp->from = radioBuffer.header.from;
             mp->to = radioBuffer.header.to;
             mp->id = radioBuffer.header.id;

src/mesh/Router.h

@@ -71,7 +71,7 @@ class Router : protected concurrency::OSThread
      * RadioInterface calls this to queue up packets that have been received from the radio.  The router is now responsible for
      * freeing the packet
      */
-    void enqueueReceivedMessage(meshtastic_MeshPacket *p);
+    virtual void enqueueReceivedMessage(meshtastic_MeshPacket *p);
 
     /**
      * Send a packet on a suitable interface.  This routine will