new_contents: # coding: utf8
  from __future__ import unicode_literals
  
  import pytest
  from spacy.tokens import Doc, DocBin
  
  
  @pytest.mark.xfail
  def test_issue4528(en_vocab):
      """Test that user_data is correctly serialized in DocBin."""
      doc = Doc(en_vocab, words=["hello", "world"])
      doc.user_data["foo"] = "bar"
      # This is how extension attribute values are stored in the user data
      doc.user_data[("._.", "foo", None, None)] = "bar"
      doc_bin = DocBin(store_user_data=True)
      doc_bin.add(doc)
      doc_bin_bytes = doc_bin.to_bytes()
      new_doc_bin = DocBin(store_user_data=True).from_bytes(doc_bin_bytes)
      new_doc = list(new_doc_bin.get_docs(en_vocab))[0]
      assert new_doc.user_data["foo"] == "bar"
      assert new_doc.user_data[("._.", "foo", None, None)] == "bar"
  
subject: Add regression test for #4528 [ci skip]