code: def test_normalize(images):
      norm_image = normalize_img_stack(images)
      for i in range(len(norm_image)):
          assert np.min(norm_image[i]) >= 0
          assert np.max(norm_image[i]) <= 1
  
file_path: pykale/tests/prepdata/test_image_transform.py
imports: import os
  import matplotlib.figure
  import numpy
  import pytest
  from numpy import testing
  from kale.interpret.visualize import plot_multi_images
  from kale.loaddata.image_access import check_dicom_series_uid, dicom2arraylist, read_dicom_dir
  from kale.prepdata.image_transform import mask_img_stack, normalize_img_stack, reg_img_stack, rescale_img_stack
label_desc: Use image node_id 6 for calling a global function with example usage: test_normalize(images) without return types