code: def test_pi_stack_voxelizer():
      current_dir = os.path.dirname(os.path.realpath(__file__))
      protein_file = os.path.join(
          current_dir, "data", "3ws9_protein_fixer_rdkit.pdb"
      )
      ligand_file = os.path.join(current_dir, "data", "3ws9_ligand.sdf")
  
      cutoff = 4.5
      box_width = 20
      voxel_width = 1.0
      voxelizer = dc.feat.PiStackVoxelizer(
          cutoff=cutoff, box_width=box_width, voxel_width=voxel_width
      )
      features = voxelizer.featurize([(ligand_file, protein_file)])
      assert features.shape == (1, box_width, box_width, box_width, 2)
  
imports: import os
  import deepchem
label_desc: Use image node_id 4 for calling a global function with example usage: test_pi_stack_voxelizer() without return types