anchor.diff:  initialize_gui_upload(ProviderSelector, UserSelector, FileGuid) ->
       UserId = oct_background:get_user_id(UserSelector),
       UserSessId = oct_background:get_user_session_id(UserSelector, ProviderSelector),
  -    Worker = oct_background:get_random_provider_node(ProviderSelector),
  -
  -    rpc:call(Worker, gs_rpc, handle, [
  +    Node = oct_background:get_random_provider_node(ProviderSelector),
  +
  +    rpc:call(Node, gs_rpc, handle, [
           ?USER(UserId, UserSessId), <<"initializeFileUpload">>, #{<<"guid">> => FileGuid}
       ]).
   
  
positive.code: 
      UserId = oct_background:get_user_id(user1),
      UserSessId = oct_background:get_user_session_id(user1, krakow),
      Worker = oct_background:get_random_provider_node(krakow),
  
      ?assertMatch(
          upload_not_authorized,
          rpc:call(Worker, page_file_upload, handle_multipart_req, [
              #{size => 20, left => 1},
              ?USER(UserId, UserSessId),
              #{
  
negative.code:     boolean().
  assert_file_uploaded(ProviderSelector, UserSelector, FileGuid, ExpSize) ->
      UserSessId = oct_background:get_user_session_id(UserSelector, ProviderSelector),
      Node = oct_background:get_random_provider_node(ProviderSelector),
  
      ?assertMatch(
          {ok, #file_attr{size = ExpSize}},
          lfm_proxy:stat(Node, UserSessId, ?FILE_REF(FileGuid)),
          ?ATTEMPTS
      ),
      {ok, FileHandle} = lfm_proxy:open(Node, UserSessId, ?FILE_REF(FileGuid), read),
      {ok, Data} = ?assertMatch({ok, _}, lfm_proxy:read(Node, FileHandle, 0, ExpSize)),
      ?assert(lists:all(fun(X) -> X == true end, [$a == Char || <<Char>> <= Data])),
      lfm_proxy:close(Node, FileHandle).
  
  
  %% @private
  -spec mock_cowboy_multipart(oct_background:entity_selector()) -> ok.
  mock_cowboy_multipart(ProviderPlaceholder) ->
      Nodes = oct_background:get_provider_nodes(ProviderPlaceholder),
      ok = test_utils:mock_new(Nodes, cow_multipart),
      ok = test_utils:mock_new(Nodes, cowboy_req),
      ok = test_utils:mock_expect(Nodes, cow_multipart, form_data,
          fun(_) -> {file, ok, ok, ok} end
      ),
      ok = test_utils:mock_expect(Nodes, cowboy_req, read_part,
          fun
              (#{done := true} = Req) ->
                  {done, Req};
  