code: def test_mask(self):
      data = {
          "img": np.array([[[0.0, 1.0], [2.0, 3.0]]]),
          "img_mask": np.array([[[1, 0], [1, 0]]], dtype=bool),
      }
      stats = IntensityStatsd(
          keys="img",
          ops=["max", "mean"],
          mask_keys="img_mask",
          key_prefix="orig",
      )
      meta = stats(data)[PostFix.meta("img")]
      np.testing.assert_allclose(meta["orig_max"], 2.0, atol=1e-3)
      np.testing.assert_allclose(meta["orig_mean"], 1.0, atol=1e-3)
  
file_path: MONAI/tests/test_intensity_statsd.py
imports: from __future__ import annotations
  import sys
  import unittest
  import numpy
  import torch.multiprocessing
  from parameterized import parameterized
  from monai.data import DataLoader, Dataset
  from monai.transforms import IntensityStatsd
  from monai.utils.enums import PostFix
label_desc: Use image node_id 3 for calling the TestIntensityStatsd obj's underlying member method code with example usage: obj.test_mask() without return types