docs: def add(self, date_range, library_name):
          """
          Adds the library with the given date range to the underlying collection of libraries used by this store.
          The underlying libraries should not overlap as the date ranges are assumed to be CLOSED_CLOSED by this function
          and the rest of the class.
  
          Arguments:
  
          date_range: A date range provided on the assumption that it is CLOSED_CLOSED. If for example the underlying
          libraries were split by year, the start of the date range would be datetime.datetime(year, 1, 1) and the end
          would be datetime.datetime(year, 12, 31, 23, 59, 59, 999000). The date range must fall on UTC day boundaries,
          that is the start must be add midnight and the end must be 1 millisecond before midnight.
  
          library_name: The name of the underlying library. This must be the name of a valid Arctic library
          """
          # check that the library is valid
          try:
              self._arctic_lib.arctic[library_name]
          except Exception as e:
              logger.error("Could not load library")
              raise e
          assert date_range.start and date_range.end, "Date range should have start and end properties {}".format(date_range)
          start = date_range.start.astimezone(mktz('UTC')) if date_range.start.tzinfo is not None else date_range.start.replace(tzinfo=mktz('UTC'))
          end = date_range.end.astimezone(mktz('UTC')) if date_range.end.tzinfo is not None else date_range.end.replace(tzinfo=mktz('UTC'))
          assert start.time() == time.min and end.time() == end_time_min, "Date range should fall on UTC day boundaries {}".format(date_range)
          # check that the date range does not overlap
          library_metadata = self._get_library_metadata(date_range)
          if len(library_metadata) > 1 or (len(library_metadata) == 1 and library_metadata[0] != library_name):
              raise OverlappingDataException("""There are libraries that overlap with the date range:
  library: {}
  overlapping libraries: {}""".format(library_name, [l.library for l in library_metadata]))
          self._collection.update_one({'library_name': library_name},
                                      {'$set': {'start': start, 'end': end}}, upsert=True)