code: def test_mask_volume():
      # Test mask volume computation
  
      mask_data = np.zeros((20, 20, 20), dtype="u1")
      mask_data[5:15, 5:15, 5:15] = 1
      img = Nifti1Image(mask_data, np.eye(4))
  
      vol_mm3 = imagestats.mask_volume(img)
      vol_vox = imagestats.count_nonzero_voxels(img)
  
      assert vol_mm3 == 1000.0
      assert vol_vox == 1000
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_mask_volume() without return types