code: def test_empty_document():
      document = build_document()
      summarizer = LuhnSummarizer()
  
      returned = summarizer(document, 10)
      assert len(returned) == 0
  
file_path: sumy/tests/test_summarizers/test_luhn.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from sumy._compat import to_unicode
  from sumy.nlp.stemmers.czech import stem_word
  from sumy.nlp.tokenizers import Tokenizer
  from sumy.parsers.plaintext import PlaintextParser
  from sumy.summarizers.luhn import LuhnSummarizer
  from sumy.utils import get_stop_words
  from ..utils import build_document
label_desc: Use image node_id 1 for calling a global function with example usage: test_empty_document() without return types