code: def test_std_non_nano(self, unit):
      dti = pd.date_range("2016-01-01", periods=55, freq="D")
      arr = np.asarray(dti).astype(f"M8[{unit}]")
  
      dta = DatetimeArray._simple_new(arr, dtype=arr.dtype)
  
      # we should match the nano-reso std, but floored to our reso.
      res = dta.std()
      assert res._creso == dta._creso
      assert res == dti.std().floor(unit)
  
imports: from __future__ import annotations
  from datetime import timedelta
  import operator
  import numpy
  import pytest
  from pandas._libs.tslibs import tz_compare
  from pandas.core.dtypes.dtypes import DatetimeTZDtype
  import pandas
  import pandas._testing
  from pandas.core.arrays import DatetimeArray, TimedeltaArray
label_desc: Use image node_id 9 for calling the TestNonNano obj's underlying member method code with example usage: obj.test_std_non_nano(unit) without return types