def test_has_invalid_chars(self):
     with self.subTest():
         self.assertEqual(EP.has_invalid_chars('&'), '&')
     with self.subTest():
         self.assertIsNone(EP.has_invalid_chars('a + b'))
     with self.subTest():
         self.assertIsNone(EP.has_invalid_chars('a * b'))
     with self.subTest():
         self.assertIsNone(EP.has_invalid_chars('a > b'))
     with self.subTest():
         self.assertIsNone(EP.has_invalid_chars('a = b'))
     with self.subTest():
         self.assertIsNone(EP.has_invalid_chars('~ b'))
     with self.subTest():
         self.assertIsNone(EP.has_invalid_chars('( b )'))