code: def test_init(self) -> None:
      obj = ClassWithDocRef()
      assert obj.document is None
  
imports: from __future__ import annotations
  import pytest
  from dataclasses import dataclass
  from bokeh.core.has_props import Local
  from bokeh.core.properties import Dict, Instance, Int, List, Nullable, Object, Tuple
  from bokeh.document import Document
  from bokeh.model import Model
  from bokeh.models import LayoutDOM, Row
  import bokeh.model.util
label_desc: Use image node_id 1 for calling the TestHasDocumentRef obj's underlying member method code with example usage: obj.test_init() without return types