added new test addressing data loader

import pytest

@pytest.mark.torch

def test_featurize():

  """Test that BertFeaturizer.featurize() correctly featurizes all sequences,

  assert (all([len(f) == 3 for f in feats]))

  assert (len(long_feat) == 1)

  assert (len(long_feat[0] == 2))

@pytest.mark.torch

def test_loading():

  """Test that the FASTA loader can load with this featurizer."""

  from transformers import BertModel, BertTokenizerFast

  from deepchem.feat.bert_tokenizer import BertFeaturizer

  from deepchem.data.data_loader import FASTALoader

  import re

  tokenizer = BertTokenizerFast.from_pretrained("Rostlab/prot_bert", do_lower_case=False)

  model = BertModel.from_pretrained("Rostlab/prot_bert")

  featurizer = BertFeaturizer(tokenizer)

  loader = FASTALoader(featurizer = featurizer, legacy = False, auto_add_annotations = True)

  data = loader.create_dataset(input_files = "../../data/tests/uniprot_truncated.fasta")

  assert data.X.shape == (61, 3, 5)