code: def test_get_ngrams():
      assert not _get_ngrams(3, "")
  
      correct_ngrams = [
          ("t", "e"),
          ("e", "s"),
          ("s", "t"),
          ("t", "i"),
          ("i", "n"),
          ("n", "g"),
      ]
      found_ngrams = _get_ngrams(2, "testing")
  
      assert len(correct_ngrams) == len(found_ngrams)
      for ngram in correct_ngrams:
          assert ngram in found_ngrams
  
file_path: sumy/tests/test_evaluation/test_evaluation_rouge.py
imports: from __future__ import absolute_import
  from __future__ import division, print_function, unicode_literals
  from pytest import approx
  from sumy.evaluation import rouge_n, rouge_l_sentence_level, rouge_l_summary_level
  from sumy.evaluation.rouge import _get_ngrams, _split_into_words, _get_word_ngrams, _len_lcs, _recon_lcs, _union_lcs
  from sumy.nlp.tokenizers import Tokenizer
  from sumy.parsers.plaintext import PlaintextParser
label_desc: Use image node_id 1 for calling a global function with example usage: test_get_ngrams() without return types