code: def test_join_preserves_freq(self, tz):
      # GH#32157
      dti = date_range("2016-01-01", periods=10, tz=tz)
      result = dti[:5].join(dti[5:], how="outer")
      assert result.freq == dti.freq
      tm.assert_index_equal(result, dti)
  
      result = dti[:5].join(dti[6:], how="outer")
      assert result.freq is None
      expected = dti.delete(5)
      tm.assert_index_equal(result, expected)
  
file_path: pandas/pandas/tests/indexes/datetimes/test_join.py
imports: from datetime import datetime, timezone
  import numpy
  import pytest
  from pandas import DataFrame, DatetimeIndex, Index, Timestamp, date_range, period_range, to_datetime
  import pandas._testing
  from pandas.tseries.offsets import BDay, BMonthEnd
label_desc: Use image node_id 10 for calling the TestJoin obj's underlying member method code with example usage: obj.test_join_preserves_freq(tz) without return types