docstr: Test writing empty data.
docstr_tok: ["Test","writing","empty","data","."]
code: def test_pad_data(self):
      """
      Test writing empty data.
      """
      sid = 1
      last_date = self.writer.last_date_in_output_for_sid(sid)
      self.assertIs(last_date, NaT)
  
      self.writer.pad(sid, TEST_CALENDAR_START)
  
      last_date = self.writer.last_date_in_output_for_sid(sid)
      self.assertEqual(last_date, TEST_CALENDAR_START)
  
      freq = self.market_opens.index.freq
      day = TEST_CALENDAR_START + freq
      minute = self.market_opens[day]
  
      data = DataFrame(
          data={
              "open": [15.0],
              "high": [17.0],
              "low": [11.0],
              "close": [15.0],
              "volume": [100.0],
          },
          index=[minute],
      )
      self.writer.write_sid(sid, data)
  
      open_price = self.reader.get_value(sid, minute, "open")
  
      self.assertEquals(15.0, open_price)
  
      high_price = self.reader.get_value(sid, minute, "high")
  
      self.assertEquals(17.0, high_price)
  
      low_price = self.reader.get_value(sid, minute, "low")
  
      self.assertEquals(11.0, low_price)
  
      close_price = self.reader.get_value(sid, minute, "close")
  
      self.assertEquals(15.0, close_price)
  
      volume_price = self.reader.get_value(sid, minute, "volume")
  
      self.assertEquals(100.0, volume_price)
  
      # Check that if we then pad the rest of this day, we end up with
      # 2 days worth of minutes.
      self.writer.pad(sid, day)
  
      self.assertEqual(
          len(self.writer._ensure_ctable(sid)),
          self.writer._minutes_per_day * 2,
      )
  
imports: from datetime import timedelta
  import os
  from numpy import arange, array, int64, float64, full, nan, transpose, zeros
  from numpy.testing import assert_almost_equal, assert_array_equal
  from pandas import DataFrame, DatetimeIndex, Timestamp, Timedelta, NaT, date_range
  from catalyst.data.minute_bars import BcolzMinuteBarMetadata, BcolzMinuteOverlappingData, US_EQUITIES_MINUTES_PER_DAY, BcolzMinuteWriterColumnMismatch, H5MinuteBarUpdateWriter, H5MinuteBarUpdateReader
  from catalyst.exchange.exchange_bcolz import BcolzExchangeBarWriter, BcolzExchangeBarReader
  from catalyst.testing.fixtures import WithAssetFinder, WithInstanceTmpDir, WithTradingCalendars, CatalystTestCase
label_desc: Use image node_id 14 for calling the BcolzMinuteBarTestCase obj's underlying member method code with example usage: obj.test_pad_data() without return types