code: def test_save_vega():
      chart = make_histogram()
      f = StringIO()
      vf.save_vega(chart, f)
      vega = json.loads(f.getvalue())
      assert (
          vega["$schema"]
          == "https://vega.github.io/schema/vega/v5.json"
      )
  
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 3 for calling a global function with example usage: test_save_vega() without return types