code: def test_gh_286():
      # https://github.com/hex-inc/vegafusion/issues/286
      vf.runtime.set_connection("datafusion")
      source = pl.from_pandas(data.seattle_weather())
  
      chart = (
          alt.Chart(source)
          .mark_bar(cornerRadiusTopLeft=3, cornerRadiusTopRight=3)
          .encode(x="month(date):O", y="count():Q", color="weather:N")
      )
      transformed = vf.transformed_data(chart)
      assert isinstance(transformed, pl.DataFrame)
      assert len(transformed) == 53
  
file_path: vegafusion/python/vegafusion/tests/test_transformed_data.py
imports: from pathlib import Path
  import pandas
  import pyarrow
  import pytest
  from altair.utils.execeval import eval_block
  import vegafusion
  from vega_datasets import data
  import polars
  import altair
label_desc: Use image node_id 5 for calling a global function with example usage: test_gh_286() without return types