anchor.diff:          [#file_block{offset = 0, size = 10}],
           [#file_block{offset = 1, size = 5}]
       ],
  -    RemoteLocation = #file_location{size = 10, space_uuid = SpaceId,
  +    RemoteLocation = #file_location{size = 10, space_id = SpaceId,
           storage_id = <<"external_storage_id">>, provider_id = ExternalProviderId,
           blocks = ExternalBlocks, file_id = ExternalFileId, uuid = FileUuid,
           version_vector = VVLocal, recent_changes = {[], ExternalChanges}},
  
positive.code:     % attach external location
      #document{value = #file_location{version_vector = VVLocal}} = rpc:call(W1, fslogic_utils, get_local_file_location, [{uuid, FileUuid}]),
      ExternalBlocks = [#file_block{offset = 2, size = 5, file_id = ExternalFileId, storage_id = <<"external_storage_id">>}],
      RemoteLocation = #file_location{size = 10, space_uuid = SpaceId,
          storage_id = <<"external_storage_id">>, provider_id = ExternalProviderId,
          blocks = ExternalBlocks, recent_changes = {[], [ExternalBlocks]}, file_id = ExternalFileId, uuid = FileUuid,
          version_vector = VVLocal},
  
negative.code:         rpc:call(W1, fslogic_utils, get_local_file_location, [{uuid, FileUuid}]),
      ExternalBlocks = [#file_block{offset = 5, size = 5}],
      ExternalSize = 10,
      RemoteLocation = #file_location{size = ExternalSize, space_id = SpaceId,
          storage_id = <<"external_storage_id">>, provider_id = ExternalProviderId,
          blocks = ExternalBlocks, file_id = ExternalFileId, uuid = FileUuid,
          version_vector = VVLocal, recent_changes = {[], [ExternalBlocks, {shrink, 7}]}},
  