code: def test_set_isolation_level(self):
      # See issue 27881.
      class CustomStr(str):
          def upper(self):
              return None
  
          def __del__(self):
              con.isolation_level = ""
  
      con = self.con
      con.isolation_level = None
      for level in "", "DEFERRED", "IMMEDIATE", "EXCLUSIVE":
          with self.subTest(level=level):
              con.isolation_level = level
              con.isolation_level = level.lower()
              con.isolation_level = level.capitalize()
              con.isolation_level = CustomStr(level)
  
      # setting isolation_level failure should not alter previous state
      con.isolation_level = None
      con.isolation_level = "DEFERRED"
      pairs = [
          (1, TypeError),
          (b"", TypeError),
          ("abc", ValueError),
          ("IMMEDIATE\0EXCLUSIVE", ValueError),
          ("\xe9", ValueError),
      ]
      for value, exc in pairs:
          with self.subTest(level=value):
              with self.assertRaises(exc):
                  con.isolation_level = value
              self.assertEqual(con.isolation_level, "DEFERRED")
  
imports: import datetime
  import unittest
  import sqlite3
  import weakref
  import functools
  from test import support
  from unittest.mock import patch
  from .util import memory_database, cx_limit
  from .util import MemoryDatabaseMixin
label_desc: Use image node_id 13 for calling the RegressionTests obj's underlying member method code with example usage: obj.test_set_isolation_level() and returns: None