code: def test_save_html():
      chart = make_histogram()
      f = StringIO()
      vf.save_html(chart, f)
      html = f.getvalue().strip()
      assert html.startswith("<!DOCTYPE html>")
      assert "https://cdn.jsdelivr.net/npm/vega@5" in html
      assert "https://cdn.jsdelivr.net/npm/vega-embed@6" in html
  
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 2 for calling a global function with example usage: test_save_html() without return types