code: def test_round2(self, tz_naive_fixture):
      tz = tz_naive_fixture
      # GH#14440 & GH#15578
      index = DatetimeIndex(
          ["2016-10-17 12:00:00.0015"], tz=tz
      ).as_unit("ns")
      result = index.round("ms")
      expected = DatetimeIndex(
          ["2016-10-17 12:00:00.002000"], tz=tz
      ).as_unit("ns")
      tm.assert_index_equal(result, expected)
  
      for freq in ["us", "ns"]:
          tm.assert_index_equal(index, index.round(freq))
  
file_path: pandas/pandas/tests/indexes/datetimes/methods/test_round.py
imports: import pytest
  from pandas._libs.tslibs import to_offset
  from pandas._libs.tslibs.offsets import INVALID_FREQ_ERR_MSG
  from pandas import DatetimeIndex, Timestamp, date_range
  import pandas._testing
label_desc: Use image node_id 4 for calling the TestDatetimeIndexRound obj's underlying member method code with example usage: obj.test_round2(tz_naive_fixture) without return types