code: def test_save_svg():
      chart = make_histogram()
      f = StringIO()
      vf.save_svg(chart, f)
      svg = f.getvalue()
      assert svg.startswith("<svg")
  
file_path: vegafusion/python/vegafusion/tests/test_save.py
imports: import altair
  from vega_datasets import data
  import vegafusion
  from io import StringIO, BytesIO
  import json
label_desc: Use image node_id 4 for calling a global function with example usage: test_save_svg() without return types