anchor.diff:                    pos_integer(), pos_integer()) -> ok.
   mark_dropped(TorrentID, Index, Offset, Length) ->
       ChunkSrv = lookup_chunk_server(TorrentID),
  -    call(ChunkSrv, {mark_dropped, self(), Index, Offset, Length}).
  +    cast(ChunkSrv, {mark_dropped, self(), Index, Offset, Length}).
   
   %% @doc
   %% Mark all currently open requests as dropped.
  
positive.code: %% with each piece. When this set is empty the piece enters the stored
  %% state. 
  %%
  
  -spec register_chunk_server(torrent_id()) -> true.
  register_chunk_server(TorrentID) ->
  
negative.code:          ?_test(mark_fetched_noop_case()),
           ?_test(mark_valid_not_stored_case()),
           ?_test(mark_valid_stored_case()),
           ?_test(all_stored_marks_stored_case()),
           ?_test(get_all_request_case())
          ]}.
  
  lookup_registered_case() ->
  