code: def test_facet(chart_type, facet_arg):
      chart = _make_chart_type(chart_type)
      if facet_arg is None:
          chart = chart.facet("color:N", columns=2)
      else:
          chart = chart.facet(**{facet_arg: "color:N", "columns": 2})
      dct = chart.to_dict()
  
      assert "spec" in dct
      assert dct["columns"] == 2
      expected = {"field": "color", "type": "nominal"}
      if facet_arg is None or facet_arg == "facet":
          assert dct["facet"] == expected
      else:
          assert dct["facet"][facet_arg] == expected
  
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 39 for calling a global function with example usage: test_facet(chart_type, facet_arg) without return types