old_contents: import unittest
  
  class TestSplitter(unittest.TestCase):
      def test_split(self):
          pass  # TODO
  
  
  class TestNLTKSplitter(unittest.TestCase):
      def test_split(self):
          pass  # TODO
  
  if __name__ == '__main__':
      unittest.main()
new_contents: import unittest
  from nala.structures.data import Dataset, Document, Part
  from nala.preprocessing.spliters import NLTKSplitter
  
  
  class TestNLTKSplitter(unittest.TestCase):
      @classmethod
      def set_up_class(cls):
          cls.dataset = Dataset()
          doc = Document()
          part = Part('This is one sentence. This is another one.\n This is the third one; here continues.')
          cls.dataset.documents['doc_1'] = doc
          doc.parts['part_1'] = part
  
      def test_split(self):
          NLTKSplitter().split(self.dataset)
          sentences = list(self.dataset.sentences())
          expected = [['This is one sentence.'], ['This is another one.'], ['This is the third one; here continues.']]
          self.assertEqual(sentences, expected)
  
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Add test for splitters