Refs #27683 -- Split up MySQL isolation level tests.

tests/backends/test_mysql.py

 import unittest
+from contextlib import contextmanager
 
 from django.core.exceptions import ImproperlyConfigured
 from django.db import connection
 from django.test import TestCase, override_settings
 
 
+@contextmanager
+def get_connection():
+    new_connection = connection.copy()
+    yield new_connection
+    new_connection.close()
+
+
 @override_settings(DEBUG=True)
 @unittest.skipUnless(connection.vendor == 'mysql', 'MySQL specific test.')
 class MySQLTests(TestCase):
 
+    read_committed = 'read committed'
+    repeatable_read = 'repeatable read'
+    isolation_values = {
+        level: level.replace(' ', '-').upper()
+        for level in (read_committed, repeatable_read)
+    }
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        configured_isolation_level = connection.isolation_level or cls.isolation_values[cls.repeatable_read]
+        cls.configured_isolation_level = configured_isolation_level.upper()
+        cls.other_isolation_level = (
+            cls.read_committed
+            if configured_isolation_level != cls.isolation_values[cls.read_committed]
+            else cls.repeatable_read
+        )
+
     @staticmethod
     def get_isolation_level(connection):
         with connection.cursor() as cursor:
@@ -25,32 +51,24 @@ class MySQLTests(TestCase):
             self.assertNotIn(query, last_query)
 
     def test_connect_isolation_level(self):
-        read_committed = 'read committed'
-        repeatable_read = 'repeatable read'
-        isolation_values = {
-            level: level.replace(' ', '-').upper()
-            for level in (read_committed, repeatable_read)
-        }
-        configured_level = connection.isolation_level or isolation_values[repeatable_read]
-        configured_level = configured_level.upper()
-        other_level = read_committed if configured_level != isolation_values[read_committed] else repeatable_read
-
-        self.assertEqual(self.get_isolation_level(connection), configured_level)
+        self.assertEqual(self.get_isolation_level(connection), self.configured_isolation_level)
 
-        new_connection = connection.copy()
-        new_connection.settings_dict['OPTIONS']['isolation_level'] = other_level
-        try:
-            self.assertEqual(self.get_isolation_level(new_connection), isolation_values[other_level])
-        finally:
-            new_connection.close()
+    def test_setting_isolation_level(self):
+        with get_connection() as new_connection:
+            new_connection.settings_dict['OPTIONS']['isolation_level'] = self.other_isolation_level
+            self.assertEqual(
+                self.get_isolation_level(new_connection),
+                self.isolation_values[self.other_isolation_level]
+            )
 
+    def test_uppercase_isolation_level(self):
         # Upper case values are also accepted in 'isolation_level'.
-        new_connection = connection.copy()
-        new_connection.settings_dict['OPTIONS']['isolation_level'] = other_level.upper()
-        try:
-            self.assertEqual(self.get_isolation_level(new_connection), isolation_values[other_level])
-        finally:
-            new_connection.close()
+        with get_connection() as new_connection:
+            new_connection.settings_dict['OPTIONS']['isolation_level'] = self.other_isolation_level.upper()
+            self.assertEqual(
+                self.get_isolation_level(new_connection),
+                self.isolation_values[self.other_isolation_level]
+            )
 
     def test_isolation_level_validation(self):
         new_connection = connection.copy()