code: def test_selected_index_none(self):
      accordion = Accordion(self.children, selected_index=None)
      state = accordion.get_state()
      assert state["selected_index"] is None
  
file_path: catboost/contrib/python/ipywidgets/py2/ipywidgets/widgets/tests/test_selectioncontainer.py
imports: from unittest import TestCase
  from traitlets import TraitError
  from ipywidgets.widgets import Accordion, HTML
label_desc: Use image node_id 2 for calling the TestAccordion obj's underlying member method code with example usage: obj.test_selected_index_none() without return types