def test_get_prep_value_empty_list(self):
     """No choice stored as empty string"""
     item = SelectMultipleField()
     self.assertIsInstance(
         item.get_prep_value([]), six.string_types)
     self.assertEquals(
         item.get_prep_value([]), '')
 def test_get_prep_value_list(self):
     item = SelectMultipleField()
     self.assertIsInstance(
         item.get_prep_value(self.choices_list), six.string_types)
 def test_get_prep_value_none(self):
     """None stored as NULL in db"""
     item = SelectMultipleField()
     self.assertIs(item.get_prep_value(None), None)