create smiles tokenizer unit test

# Requriments - transformers, tokenizers

from unittest import TestCase

from deepchem.feat.smiles_tokenizer import SmilesTokenizer

from transformers import RobertaForMaskedLM

class TestSmilesTokenizer(TestCase):

  """Tests the SmilesTokenizer to load the USPTO vocab file and a ChemBERTa Masked LM model with pre-trained weights.."""

  def test_featurize(self):

    from rdkit import Chem

    smiles = ["Cn1c(=O)c2c(ncn2C)n(C)c1=O", "CC(=O)N1CN(C(C)=O)C(O)C1O"]

    mols = [Chem.MolFromSmiles(smile) for smile in smiles]

    featurizer = dc.feat.one_hot.OneHotFeaturizer(dc.feat.one_hot.zinc_charset)

    one_hots = featurizer.featurize(mols)

    untransformed = featurizer.untransform(one_hots)

    assert len(smiles) == len(untransformed)

    for i in range(len(smiles)):

      assert smiles[i] == untransformed[i][0]