code: def test_dateindex_conversion(self, freq, dtc):
      rtol = 10**-9
      dateindex = date_range("2020-01-01", periods=10, freq=freq)
      rs = dtc.convert(dateindex, None, None)
      xp = converter.mdates.date2num(dateindex._mpl_repr())
      tm.assert_almost_equal(rs, xp, rtol=rtol)
  
imports: from datetime import date, datetime
  import subprocess
  import sys
  import numpy
  import pytest
  import pandas._config.config
  from pandas._libs.tslibs import to_offset
  from pandas import Index, Period, PeriodIndex, Series, Timestamp, arrays, date_range
  import pandas._testing
  from pandas.plotting import deregister_matplotlib_converters, register_matplotlib_converters
  from pandas.tseries.offsets import Day, Micro, Milli, Second
label_desc: Use image node_id 7 for calling the TestDateTimeConverter obj's underlying member method code with example usage: obj.test_dateindex_conversion(freq, dtc) without return types