test(spanner): disable pooling in mock server tests

Author: chalmerlowe

packages/sqlalchemy-spanner/tests/mockserver_tests/mock_server_test_base.py

@@ -161,9 +161,12 @@ def teardown_method(self):
         MockServerTestBase.database_admin_service.clear_requests()
 
     def create_engine(self) -> Engine:
+        from sqlalchemy.pool import NullPool
+
         return create_engine(
             "spanner:///projects/p/instances/i/databases/d",
             connect_args={"client": self.client, "logger": MockServerTestBase.logger},
+            poolclass=NullPool,  # Disable pooling to force new sessions for every test
         )
 
     @property