old_contents: # -*- coding: UTF-8 -*-
  
  from core import serialize
  import pandas
  
  
  df = pandas.DataFrame([{"a": 1, "b": 2, "c": 3}, {"a": 2, "b": 4, "c": 6}])
  
  
  def test_type():
      assert type(serialize(df, render_to="chart")) is str
      assert type(serialize(df, x="a", render_to="chart")) is str
      assert type(serialize(df, x="a", y=("b",), render_to="chart")) is str
      assert type(serialize(df, figsize=(100, 100), render_to="chart")) is str
  
new_contents: # -*- coding: UTF-8 -*-
  
  from core import serialize
  import pandas
  from unittest import TestCase
  
  df = pandas.DataFrame([{"a": 1, "b": 2, "c": 3}, {"a": 2, "b": 4, "c": 6}])
  
  
  class CoreTest(TestCase):
      def test_type(self):
          self.assertIsInstance(serialize(df, render_to="chart"), str)
          obj = serialize(df, render_to="chart", output_type="json")
          self.assertIsInstance(obj, dict)
          obj = serialize(df, render_to="chart", output_type="json", zoom="xy")
          self.assertIn("chart", obj)
          self.assertIsInstance(obj["chart"], dict)
          self.assertIn("zoomType", obj["chart"])
          self.assertRaises(ValueError, serialize, df, **{"render_to": "chart", "zoom": "z"})
          obj = serialize(df, render_to="chart", output_type="json", kind="bar")
          self.assertIn("chart", obj)
          self.assertIsInstance(obj["chart"], dict)
          self.assertEqual(obj["chart"].get("type"), "column")
          self.assertRaises(ValueError, serialize, df, **{"render_to": "chart", "kind": "z"})
          obj = serialize(df, render_to="chart", output_type="json", secondary_y="a")
          self.assertTrue(obj.get("yAxis", [])[1].get('opposite'))
          obj = serialize(df, render_to="chart", output_type="json", rot=45)
          # self.assertTrue(False)
          # assert type(serialize(df, x="a", render_to="chart")) is str
          # assert type(serialize(df, x="a", y=("b",), render_to="chart")) is str
          # assert type(serialize(df, figsize=(100, 100), render_to="chart")) is str
  
subject: use unittest module