anchor.diff:                                        , Config
                                         , DefaultConsumerConfig
                                         ),
  -  start_subscriber(Config, Topics, GroupConfig, ConsumerConfig, InitArgs).
  -
  -start_subscriber(Config, Topics, GroupConfig, ConsumerConfig, InitArgs) ->
  -  GroupId = case ?config(group_id) of
  -              undefined -> ?group_id;
  -              A         -> A
  -            end,
  +  start_subscriber(GroupId, Config, Topics, GroupConfig, ConsumerConfig, InitArgs).
  +
  +start_subscriber(GroupId, Config, Topics, GroupConfig, ConsumerConfig, InitArgs) ->
     {ok, SubscriberPid} =
       case ?config(behavior) of
        brod_group_subscriber_v2 ->
  
positive.code:      begin
         %% Produce some messages into the topic:
         {_, L} = produce_payloads(Topic, Partition, Config),
         {ok, SubscriberPid} = start_subscriber(Config, [Topic], InitArgs),
         %% And ack/commit them asynchronously:
         [begin
            {ok, #{offset := Offset}} = ?wait_message(Topic, Partition, I, _),
  
negative.code:      #{ timeout => 5000 },
       %% Run stage:
       begin
         {ok, SubscriberPid} = start_subscriber(?group_id, Config, [Topic], InitArgs),
         %% Send a message to the topic and wait until it's received to make sure the subscriber is stable:
         produce({Topic, Partition}, <<0>>),
         {ok, _} = ?wait_message(Topic, Partition, <<0>>, _),
  