code: def test_get_formatting_func_from_dataset_with_unknown_format(self):
      dataset = Dataset.from_dict({"text": "test"})
      formatting_func = get_formatting_func_from_dataset(
          dataset, self.llama_tokenizer
      )
      self.assertIsNone(formatting_func)
  
file_path: trl/tests/test_dataset_formatting.py
imports: import unittest
  from typing import Callable
  from datasets import Dataset, load_dataset
  from transformers import AutoTokenizer
  from trl.extras.dataset_formatting import get_formatting_func_from_dataset
label_desc: Use image node_id 6 for calling the DatasetFormattingTestCase obj's underlying member method code with example usage: obj.test_get_formatting_func_from_dataset_with_unknown_format() without return types