code: def test_mapper_disconnected_compounds():
      """
      Test '[I-].[K+]' in _MapperDMPNN (disconnected compounds)
      """
      mapper = _MapperDMPNN(graphs[4])
      assert (mapper.bond_to_ini_atom == np.empty(0)).all()
      assert (
          mapper.atom_to_incoming_bonds == np.asarray([[-1], [-1]])
      ).all()
      assert (mapper.mapping == np.asarray([[-1]])).all()
  
file_path: deepchem/deepchem/models/tests/test_mapper_dmpnn.py
imports: from deepchem.feat import DMPNNFeaturizer
  import numpy
  import pytest
label_desc: Use image node_id 6 for calling a global function with example usage: test_mapper_disconnected_compounds() without return types