code: def _count_ImageOpeners(proxy, data, voxels):
      CountingImageOpener.num_openers = 0
      # expected data is defined in the test_keep_file_open_* tests
      for i in range(voxels.shape[0]):
          x, y, z = (int(c) for c in voxels[i, :])
          assert proxy[x, y, z] == x * 100 + y * 10 + z
      return CountingImageOpener.num_openers
  
imports: import contextlib
  import gzip
  import pickle
  from io import BytesIO
  from unittest import mock
  import numpy
  import pytest
  from numpy.testing import assert_array_almost_equal, assert_array_equal
  from packaging.version import Version
  from ..None import __version__
  from ..arrayproxy import ArrayProxy, get_obj_dtype, is_proxy, reshape_dataobj
  from ..deprecator import ExpiredDeprecationError
  from ..nifti1 import Nifti1Header, Nifti1Image
  from ..openers import ImageOpener
  from ..testing import memmap_after_ufunc
  from ..tmpdirs import InTemporaryDirectory
  from .test_fileslice import slicer_samples
  from .test_openers import patch_indexed_gzip
label_desc: Use image node_id 16 for calling a global function with example usage: _count_ImageOpeners(proxy, data, voxels) and returns: CountingImageOpener