diff --git a/src/govoplan_addresses/backend/service.py b/src/govoplan_addresses/backend/service.py
index 3109372..33b3e88 100644
--- a/src/govoplan_addresses/backend/service.py
+++ b/src/govoplan_addresses/backend/service.py
@@ -99,7 +99,7 @@ REMOTE_SYNC_ACTIONS = {"remote_create", "remote_update", "remote_delete"}
 ADDRESS_MODULE_ID = "addresses"
 ADDRESS_CONTACTS_COLLECTION = "addresses.contacts"
 ADDRESS_CONTACT_RESOURCE = "address_contact"
-CARDDAV_SECRET_ENV_PREFIX = "env:"
+CARDDAV_SECRET_ENV_PREFIX = "env:"  # noqa: S105  # nosec B105 - reference prefix, not a credential.
 
 
 def _trim(value: str | None) -> str | None:
diff --git a/tests/test_addresses_service.py b/tests/test_addresses_service.py
index cfe945e..2f3b22c 100644
--- a/tests/test_addresses_service.py
+++ b/tests/test_addresses_service.py
@@ -158,9 +158,9 @@ class AddressBookAdminPrincipal(NoGroupPrincipal):
 
 class AddressServiceTest(unittest.TestCase):
     def setUp(self) -> None:
-        engine = create_engine("sqlite:///:memory:")
+        self.engine = create_engine("sqlite:///:memory:")
         Base.metadata.create_all(
-            engine,
+            self.engine,
             tables=[
                 AddressBook.__table__,
                 AddressList.__table__,
@@ -176,9 +176,14 @@ class AddressServiceTest(unittest.TestCase):
                 ChangeSequenceEntry.__table__,
             ],
         )
-        self.session = sessionmaker(bind=engine)()
+        self.session = sessionmaker(bind=self.engine)()
         self.principal = Principal()
 
+    def tearDown(self) -> None:
+        self.session.close()
+        Base.metadata.drop_all(bind=self.engine)
+        self.engine.dispose()
+
     def test_group_book_creation_requires_membership_or_admin_scope(self) -> None:
         with self.assertRaisesRegex(AddressBookError, "selected group is not visible"):
             create_address_book(