code: def test_fit_with_validation_set(self):
      train = random_transformer_dataset(8)
      valid = random_transformer_dataset(2)
  
      model_args = TransformerModelArguments(
          "sshleifer/tiny-distilroberta-base"
      )
      classifier = TransformerBasedClassification(model_args, 2)
      with patch.object(classifier, "_fit_main") as fit_main_mock:
          classifier.fit(train, validation_set=valid)
          fit_main_mock.assert_called()
          self.assertIsNone(classifier.class_weights_)
  
          call_args = fit_main_mock.call_args[0]
          self.assertTrue(isinstance(call_args[0], TransformersDataset))
          self.assertTrue(isinstance(call_args[1], TransformersDataset))
  
          self.assertEqual(len(train), len(call_args[0]))
          self.assertEqual(len(valid), len(call_args[1]))
  
imports: import unittest
  import pytest
  import numpy
  from unittest.mock import patch
  from small_text.base import LABEL_UNLABELED
  from small_text.integrations.pytorch.exceptions import PytorchNotFoundError
  from small_text.training.early_stopping import EarlyStopping, EarlyStoppingOrCondition
  from small_text.training.metrics import Metric
  from small_text.utils.logging import VERBOSITY_MORE_VERBOSE
label_desc: Use image node_id 6 for calling the TestTransformerBasedClassification obj's underlying member method code with example usage: obj.test_fit_with_validation_set() without return types