test: fix assertions

apps/emqx/test/emqx_persistent_messages_SUITE.erl

@@ -132,19 +132,18 @@ t_session_subscription_iterators(Config) ->
             ct:pal("publishing 1"),
             Message1 = emqx_message:make(Topic, Payload1),
             publish(Node1, Message1),
-            receive_messages(1),
             ct:pal("subscribing 1"),
             {ok, _, [2]} = emqtt:subscribe(Client, SubTopicFilter, qos2),
             ct:pal("publishing 2"),
             Message2 = emqx_message:make(Topic, Payload2),
             publish(Node1, Message2),
-            receive_messages(1),
+            [_] = receive_messages(1),
             ct:pal("subscribing 2"),
             {ok, _, [1]} = emqtt:subscribe(Client, SubTopicFilter, qos1),
             ct:pal("publishing 3"),
             Message3 = emqx_message:make(Topic, Payload3),
             publish(Node1, Message3),
-            receive_messages(1),
+            [_] = receive_messages(1),
             ct:pal("publishing 4"),
             Message4 = emqx_message:make(AnotherTopic, Payload4),
             publish(Node1, Message4),