Mixed version test fix

deps/rabbitmq_mqtt/test/command_SUITE.erl

@@ -57,7 +57,23 @@ init_per_group(unit, Config) ->
     Config;
 init_per_group(Group, Config) ->
     Config1 = rabbit_ct_helpers:set_config(Config, {mqtt_version, Group}),
-    util:maybe_skip_v5(Config1).
+    case Group of
+        v4 ->
+            AllApps = rabbit_ct_broker_helpers:rpc_all(Config1, application, loaded_applications, []),
+            AllAppNames = lists:map(fun (AppList) ->
+               lists:map(fun ({Name, _, _}) -> Name end, AppList)
+            end, AllApps),
+            case lists:all(fun (NodeApps) ->
+                lists:member(rabbit_web_mqtt_app, NodeApps)
+            end, AllAppNames) of
+                true ->
+                    Config1;
+                false ->
+                    {skip, "rabbit_web_mqtt_app not available on all nodes"}
+            end;
+        v5 ->
+            util:maybe_skip_v5(Config1)
+    end.
 
 end_per_group(_, Config) ->
     Config.