code: def test_selected_is_readonly(self) -> None:
      ds = bms.ColumnDataSource()
      with pytest.raises(RuntimeError) as e:
          ds.selected = Selection()
          assert str(e).endswith(
              "ColumnDataSource.selected is a readonly property"
          )
  
imports: from __future__ import annotations
  import pytest
  import datetime
  import io
  import numpy
  import pandas
  from bokeh.models import Selection
  from bokeh.util.serialization import convert_datetime_array
  from bokeh.util.warnings import BokehDeprecationWarning
  import bokeh.models.sources
label_desc: Use image node_id 2 for calling the TestColumnDataSource obj's underlying member method code with example usage: obj.test_selected_is_readonly() without return types