code: def test_freq_setter(self, values, freq, tz):
      # GH#20678
      idx = DatetimeIndex(values, tz=tz)
  
      # can set to an offset, converting from string if necessary
      idx._data.freq = freq
      assert idx.freq == freq
      assert isinstance(idx.freq, DateOffset)
  
      # can reset to None
      idx._data.freq = None
      assert idx.freq is None
  
imports: import pytest
  from pandas import DatetimeIndex, date_range
  from pandas.tseries.offsets import BDay, DateOffset, Day, Hour
label_desc: Use image node_id 2 for calling the TestFreq obj's underlying member method code with example usage: obj.test_freq_setter(values, freq, tz) without return types