code: def test_backpointer(nlp_pipeline):
      doc = nlp_pipeline(EN_DOC2)
      ent = doc.ents[0]
      assert ent.sent is doc.sentences[0]
      assert list(doc.iter_words())[0].sent is doc.sentences[0]
      assert list(doc.iter_tokens())[-1].sent is doc.sentences[-1]
  
file_path: stanza/stanza/tests/common/test_data_objects.py
imports: import pytest
  import stanza
  from stanza.models.common.doc import Document, Sentence, Word
  from stanza.tests import *
label_desc: Use image node_id 5 for calling a global function with example usage: test_backpointer(nlp_pipeline) without return types