code: def expected_bar_value(asset_id, date, colname):
      
      from_asset = asset_id * 100000
      from_colname = OHLCV.index(colname) * 1000
      from_date = (date - PSEUDO_EPOCH).days
      return from_asset + from_colname + from_date
docs: Check that the raw value for an asset/date/column triple is as
      expected.
  
      Used by tests to verify data written by a writer.