new_contents: import datetime
  import json
  import unittest
  
  from clippings.utils import DatetimeJSONEncoder
  
  
  DATE = datetime.datetime(2016, 1, 2, 3, 4, 5)
  DATE_STRING = "2016-01-02T03:04:05"
  
  
  class DatetimeJSONEncoderTest(unittest.TestCase):
  
      def test_datetime_encoder_format(self):
          dictionary = {"now": DATE}
          expected_json_string = json.dumps({"now": DATE_STRING})
          json_string = json.dumps(dictionary, cls=DatetimeJSONEncoder)
          self.assertEqual(expected_json_string, json_string)
  
      def test_datetime_encoder_typeerror(self):
          undumpable_dictionary = {"set": set()}
          # Ensure we let the parent raise TypeError
          with self.assertRaises(TypeError):
              json_string = json.dumps(undumpable_dictionary, cls=DatetimeJSONEncoder)
  
subject: Add basic test for DatetimeJSONEncoder