anchor.diff:                    pos_integer(), pos_integer()) -> ok.
   mark_stored(TorrentID, Index, Offset, Length) ->
       ChunkSrv = lookup_chunk_server(TorrentID),
  -    Call = {mark_stored, self(), Index, Offset, Length},
  -    gen_server:call(ChunkSrv, Call).
  +    call(ChunkSrv, {mark_stored, self(), Index, Offset, Length}).
   
   %& @doc
   %% Reinsert a chunk into the request queue.
  
positive.code:     gen_server:start_link(?MODULE, [TorrentID, ChunkSize, Fetched, Sizes], []).
  
  %% @doc
  %% Mark a chunk as fetched but not written to file.
  %% @end
  -spec mark_fetched(torrent_id(), pos_integer(),
                     pos_integer(), pos_integer()) -> {ok, list(pid())}.
  mark_fetched(TorrentID, Index, Offset, Length) ->
      ChunkSrv = lookup_chunk_server(TorrentID),
      Call = {mark_fetched, self(), Index, Offset, Length},
      gen_server:call(ChunkSrv, Call).
  
  %& @doc
  %% Mark a chunk as fetched and written to file.
  
negative.code:          ?_test(drop_none_on_exit_case()),
           ?_test(drop_all_on_exit_case()),
           ?_test(marked_stored_not_dropped_case()),
           ?_test(mark_fetched_noop_case()),
           ?_test(mark_valid_not_stored_case()),
           ?_test(mark_valid_stored_case())
          ]}.
  
  lookup_registered_case() ->
  