code: def test_zerostd(self):
      key = "img"
      image = np.ones([2, 3, 3])
      for nonzero in [True, False]:
          for channel_wise in [True, False]:
              factor = np.random.rand()
              std_shifter = StdShiftIntensityd(
                  keys=[key],
                  factor=factor,
                  nonzero=nonzero,
                  channel_wise=channel_wise,
              )
              result = std_shifter({key: image})
              np.testing.assert_allclose(result[key], image, rtol=1e-5)
  
file_path: MONAI/tests/test_std_shift_intensityd.py
imports: from __future__ import annotations
  import unittest
  import numpy
  from monai.transforms import ShiftIntensityd, StdShiftIntensityd
  from monai.utils import dtype_numpy_to_torch
  from tests.utils import NumpyImageTestCase2D
label_desc: Use image node_id 2 for calling the TestStdShiftIntensityd obj's underlying member method code with example usage: obj.test_zerostd() without return types