code: def test_iteration_preserves_nanoseconds(self, tz):
      # GH#19603
      index = DatetimeIndex(
          [
              "2018-02-08 15:00:00.168456358",
              "2018-02-08 15:00:00.168456359",
          ],
          tz=tz,
      )
      for i, ts in enumerate(index):
          assert ts == index[i]
  
file_path: pandas/pandas/tests/indexes/datetimes/test_iter.py
imports: import dateutil.tz
  import numpy
  import pytest
  from pandas import DatetimeIndex, date_range, to_datetime
  from pandas.core.arrays import datetimes
label_desc: Use image node_id 1 for calling the TestDatetimeIndexIteration obj's underlying member method code with example usage: obj.test_iteration_preserves_nanoseconds(tz) without return types