MQTT auth_SUITE: terminate setup process

Configuring the mock authentication backend blocks
and generates an error in the test process when the
broker goes down. The error report makes the test fail
in some environments.

The process where the setup takes place must stay up
otherwise the ETS table used will go away.

This commit makes sure the broker-side authentication backend
setup returns at the end of the test. This way the calling
process terminates in a normal way.

deps/rabbitmq_mqtt/test/auth_SUITE.erl

@@ -526,8 +526,8 @@ client_id_propagation(Config) ->
                   rpc(Config, 0, rabbit_auth_backend_mqtt_mock, setup, [Self])
           end),
     %% the setup process will notify us
-    receive
-        ok -> ok
+    SetupProcess = receive
+        {ok, SP} -> SP
     after
         3000 -> ct:fail("timeout waiting for rabbit_auth_backend_mqtt_mock:setup/1")
     end,
@@ -561,7 +561,11 @@ client_id_propagation(Config) ->
     VariableMap = maps:get(variable_map, TopicContext),
     ?assertEqual(ClientId, maps:get(<<"client_id">>, VariableMap)),
 
-    ok = emqtt:disconnect(C).
+    ok = emqtt:disconnect(C),
+
+    SetupProcess ! stop,
+
+    ok.
 
 %% These tests try to cover all operations that are listed in the
 %% table in https://www.rabbitmq.com/access-control.html#authorisation

deps/rabbitmq_mqtt/test/rabbit_auth_backend_mqtt_mock.erl

@@ -21,7 +21,7 @@
 
 setup(CallerPid) ->
     ets:new(?MODULE, [set, public, named_table]),
-    CallerPid ! ok,
+    CallerPid ! {ok, self()},
     receive
         stop -> ok
     end.