anchor.diff:    receive
       {change, Change} ->
         collect_changes(I-1, queue:in(Change, Q))
  -  end.+  end.
  +
  +wait_pids([]) -> ok;
  +wait_pids(Pids) ->
  +  receive
  +    {ok, Pid} -> wait_pids(Pids -- [Pid])
  +  after 5000 -> {error, receive_pids}
  +  end.
  
positive.code:   [#{ <<"seq">> := 1, <<"id">> := <<"aa">>}] = barrel_httpc_changes:changes(Pid),
    [] = barrel_httpc_changes:changes(Pid),
    ok = barrel_httpc_changes:stop(Pid).
    
  collect_changes(0, Q) ->
    queue:to_list(Q);
  
negative.code:     #{ <<"seq">> := 3, <<"id">> := <<"cc">>},
      #{ <<"seq">> := 4, <<"id">> := <<"dd">>}
    ] = barrel_httpc_changes:changes(Pid),
    ok = barrel_httpc_changes:stop(Pid).
  
  changes_feed_callback(Config) ->
    Self = self(),
  