code: def test_selection_expression():
      data = pd.DataFrame([{"a": "A", "b": 28}])
  
      sel = alt.selection_point(fields=["b"])
      se = sel.b | 300
  
      assert isinstance(se, alt.SelectionExpression)
      assert isinstance(se.expr, alt.expr.core.Expression)
  
      c = (
          alt.Chart(data)
          .mark_point()
          .encode(
              x="a:N",
              y="b:Q",
              size=alt.value(se),
          )
          .add_params(sel)
      )
  
      dct = c.to_dict()
      expr_str = str(se.expr)
  
      assert dct["encoding"]["size"]["value"]["expr"] == expr_str
  
file_path: altair/tests/vegalite/v5/test_params.py
imports: import pandas
  import warnings
  import pytest
  import re
  import altair.vegalite.v5
label_desc: Use image node_id 5 for calling a global function with example usage: test_selection_expression() without return types