code: def test_selection_expression():
      selection = alt.selection_point(fields=["value"])
  
      assert isinstance(selection.value, alt.SelectionExpression)
      assert selection.value.to_dict() == {
          "expr": f"{selection.name}.value"
      }
  
      assert isinstance(selection["value"], alt.expr.Expression)
      assert selection["value"].to_dict() == "{0}['value']".format(
          selection.name
      )
  
      magic_attr = "__magic__"
      with pytest.raises(AttributeError):
          getattr(selection, magic_attr)
  
imports: import io
  import json
  import operator
  import os
  import pathlib
  import tempfile
  import jsonschema
  import pytest
  import pandas
  import altair.vegalite.v5
label_desc: Use image node_id 9 for calling a global function with example usage: test_selection_expression() without return types