code: def test_LookupData():
      df = pd.DataFrame({"x": [1, 2, 3], "y": [4, 5, 6]})
      lookup = alt.LookupData(data=df, key="x")
  
      dct = lookup.to_dict()
      assert dct["key"] == "x"
      assert dct["data"] == {
          "values": [
              {"x": 1, "y": 4},
              {"x": 2, "y": 5},
              {"x": 3, "y": 6},
          ]
      }
  
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 27 for calling a global function with example usage: test_LookupData() without return types