spec that check qos0 msgs are not published if no client is subscribed

spec/mqtt/integrations/message_qos_spec.cr

@@ -260,5 +260,29 @@ module MqttSpecs
         end
       end
     end
+
+    it "should not enqueue messages with QoS 0 if no client is subscribed to the session" do
+      with_server do |server|
+        with_client_io(server) do |io|
+          connect(io)
+          topic_filters = mk_topic_filters({"a/b", 0u8})
+          subscribe(io, topic_filters: topic_filters)
+          disconnect(io)
+        end
+
+        with_client_io(server) do |publisher_io|
+          connect(publisher_io, client_id: "publisher")
+          publish(publisher_io, topic: "a/b", qos: 0u8)
+          disconnect(publisher_io)
+        end
+
+        with_client_io(server) do |io|
+          connect(io)
+          pkt = read_packet(io)
+          pkt.should be_nil
+          disconnect(io)
+        end
+      end
+    end
   end
 end