anchor.diff:  
       fetch_many(Refs, Worker1, notify_fun(), on_complete_fun(CounterPid)),
   
  -    %% then
  +    timer:sleep(?TIMEOUT),
       stop_counter(CounterPid),
  +    %% then
       ?assertReceivedMatch(
           {counterOnComplete, {ok, RequestsNum}, {erros, 0}}, ?TIMEOUT).
   
  
positive.code:         [Ref1, notify_fun(), on_complete_fun(self())]
      ),
  
  %%     then
      ?assertReceivedMatch({on_complete, {error, test_error}}, ?TIMEOUT).
  
  error_write_fun_test(Config) ->
      %% test with write_fun callback returning an error
      [Worker1, Worker2 | _] = ?config(op_worker_nodes, Config),
  
      %% given
      DataSize = 1024 * ?TEST_BLOCK_SIZE,
      Data = generate_binary(DataSize),
      WriteFunOpt = make_opt_fun(write_fun, {error, ?FILE_HANDLE2, test_error}),
      ReadFunOpt = make_opt_fun(read_fun, {ok, ?FILE_HANDLE2, Data}),
  
negative.code:     ),
      remote_apply(Worker1, rtransfer, cancel, [Ref1]),
  
      timer:sleep(?TIMEOUT),
      %% then
      ?assertReceivedMatch({on_complete, {error, canceled}}, ?TIMEOUT).
  
  %% TODO...
  many_requests_test(Config) ->
      %% test fetching many files
      [Worker1, Worker2 | _] = ?config(op_worker_nodes, Config),
  