code: def test_iter(self) -> None:
      d = Document()
      dm = bdm.DocumentModelManager(d)
      assert len(dm) == 0
  
      m1 = Div()
      m2 = Div()
      m3 = Div()
  
      dm["m1"] = m1
      dm["m2"] = m2
      dm["m3"] = m3
  
      result = set()
      for m in dm:
          result.add(m)
  
      assert result == {m1, m2, m3}
  
imports: from __future__ import annotations
  import pytest
  import gc
  from unittest.mock import MagicMock, patch
  from bokeh.core.has_props import Local
  from bokeh.core.properties import Instance, Nullable
  from bokeh.core.types import ID
  from bokeh.document import Document
  from bokeh.model import Model
  from bokeh.models import Div, Row
  import bokeh.document.models
label_desc: Use image node_id 5 for calling the TestDocumentModelManager obj's underlying member method code with example usage: obj.test_iter() without return types