gh-105539: Explict resource management for connection objects in sqlite3 tests (#108017)

- Use memory_database() helper
- Move test utility functions to util.py
- Add convenience memory database mixin
- Add check() helper for closed connection tests

Lib/test/test_sqlite3/test_transactions.py

@@ -28,7 +28,8 @@
 from test.support.os_helper import TESTFN, unlink
 from test.support.script_helper import assert_python_ok
 
-from test.test_sqlite3.test_dbapi import memory_database
+from .util import memory_database
+from .util import MemoryDatabaseMixin
 
 
 TIMEOUT = LOOPBACK_TIMEOUT / 10
@@ -132,14 +133,14 @@ def test_locking(self):
 
     def test_rollback_cursor_consistency(self):
         """Check that cursors behave correctly after rollback."""
-        con = sqlite.connect(":memory:")
-        cur = con.cursor()
-        cur.execute("create table test(x)")
-        cur.execute("insert into test(x) values (5)")
-        cur.execute("select 1 union select 2 union select 3")
+        with memory_database() as con:
+            cur = con.cursor()
+            cur.execute("create table test(x)")
+            cur.execute("insert into test(x) values (5)")
+            cur.execute("select 1 union select 2 union select 3")
 
-        con.rollback()
-        self.assertEqual(cur.fetchall(), [(1,), (2,), (3,)])
+            con.rollback()
+            self.assertEqual(cur.fetchall(), [(1,), (2,), (3,)])
 
     def test_multiple_cursors_and_iternext(self):
         # gh-94028: statements are cleared and reset in cursor iternext.
@@ -218,10 +219,7 @@ def test_no_duplicate_rows_after_rollback_new_query(self):
 
 
 
-class SpecialCommandTests(unittest.TestCase):
-    def setUp(self):
-        self.con = sqlite.connect(":memory:")
-        self.cur = self.con.cursor()
+class SpecialCommandTests(MemoryDatabaseMixin, unittest.TestCase):
 
     def test_drop_table(self):
         self.cur.execute("create table test(i)")
@@ -233,14 +231,8 @@ def test_pragma(self):
         self.cur.execute("insert into test(i) values (5)")
         self.cur.execute("pragma count_changes=1")
 
-    def tearDown(self):
-        self.cur.close()
-        self.con.close()
 
-
-class TransactionalDDL(unittest.TestCase):
-    def setUp(self):
-        self.con = sqlite.connect(":memory:")
+class TransactionalDDL(MemoryDatabaseMixin, unittest.TestCase):
 
     def test_ddl_does_not_autostart_transaction(self):
         # For backwards compatibility reasons, DDL statements should not
@@ -268,9 +260,6 @@ def test_transactional_ddl(self):
         with self.assertRaises(sqlite.OperationalError):
             self.con.execute("select * from test")
 
-    def tearDown(self):
-        self.con.close()
-
 
 class IsolationLevelFromInit(unittest.TestCase):
     CREATE = "create table t(t)"