code: def test_separation():
      """Tests the reagent separation feature after tokenizing the reactions.
      The tokenized reaction is decoded before testing for equality, to make the
      test more readable.
      """
      from transformers import RobertaTokenizerFast
      from deepchem.feat.reaction_featurizer import RxnFeaturizer
  
      tokenizer = RobertaTokenizerFast.from_pretrained(
          "seyonec/PubChem10M_SMILES_BPE_450k"
      )
      featurizer_mix = RxnFeaturizer(tokenizer, sep_reagent=False)
      featurizer_sep = RxnFeaturizer(tokenizer, sep_reagent=True)
      reaction = [
          "CCS(=O)(=O)Cl.OCCBr>CCN(CC)CC.CCOCC>CCS(=O)(=O)OCCBr"
      ]
      feats_mix = featurizer_mix.featurize(reaction)
      feats_sep = featurizer_sep.featurize(reaction)
  
      # decode the source in the mixed and separated cases
      mix_decoded = tokenizer.decode(feats_mix[0][0][0][0]).replace(
          "<pad>", ""
      )
      sep_decoded = tokenizer.decode(feats_sep[0][0][0][0]).replace(
          "<pad>", ""
      )
      assert (
          mix_decoded == "<s>CCS(=O)(=O)Cl.OCCBr.CCN(CC)CC.CCOCC></s>"
      )
      assert sep_decoded == "<s>CCS(=O)(=O)Cl.OCCBr>CCN(CC)CC.CCOCC</s>"
  
label_desc: Use image node_id 2 for calling a global function with example usage: test_separation() without return types