code: def test_nonzero(self):
      key = "img"
      image = np.asarray([[4.0, 0.0, 2.0], [0, 2, 4]])  # std = 1
      factor = np.random.rand()
      std_shifter = StdShiftIntensityd(
          keys=[key], factor=factor, nonzero=True
      )
      result = std_shifter({key: image})
      expected = np.asarray(
          [[4 + factor, 0, 2 + factor], [0, 2 + factor, 4 + factor]]
      )
      np.testing.assert_allclose(result[key], expected, 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 3 for calling the TestStdShiftIntensityd obj's underlying member method code with example usage: obj.test_nonzero() without return types