PYTHON-5672 Fix test_client_checkout_setup_failure on freethreaded Python

patch.object cannot shadow a method on an instance when __slots__ is
defined — the attribute is read-only. Use a subclass override instead.

Author: blink1073

test/asynchronous/test_client.py

@@ -822,21 +822,23 @@ async def test_client_checkout_setup_failure_returns_connection(self):
         # Verify that the connection is returned to the pool when an exception
         # is raised during _ClientCheckout.__aenter__ post-checkout setup
         # (e.g. session pinning or the auto-encryption wire-version check).
-        from unittest.mock import patch
-
+        # Use a subclass to override contribute_socket because __slots__ prevents
+        # instance-level patching of methods.
         from pymongo.asynchronous.mongo_client import _ClientCheckout
 
+        class _BrokenSetupCheckout(_ClientCheckout):
+            def contribute_socket(self, conn, completed_handshake=True):
+                raise RuntimeError("simulated failure in post-checkout setup")
+
         client = await self.async_rs_or_single_client()
         server = await (await client._get_topology()).select_server(
             writable_server_selector, _Op.TEST
         )
         pool = server.pool
 
-        checkout = _ClientCheckout(client, server, None)
-        with patch.object(checkout, "contribute_socket", side_effect=RuntimeError("simulated")):
-            with self.assertRaises(RuntimeError):
-                async with checkout:
-                    pass
+        with self.assertRaises(RuntimeError):
+            async with _BrokenSetupCheckout(client, server, None):
+                pass
 
         # Connection was returned to pool, not leaked.
         self.assertEqual(0, pool.active_sockets)

test/test_client.py

@@ -797,19 +797,21 @@ def test_client_checkout_setup_failure_returns_connection(self):
         # Verify that the connection is returned to the pool when an exception
         # is raised during _ClientCheckout.__aenter__ post-checkout setup
         # (e.g. session pinning or the auto-encryption wire-version check).
-        from unittest.mock import patch
-
+        # Use a subclass to override contribute_socket because __slots__ prevents
+        # instance-level patching of methods.
         from pymongo.synchronous.mongo_client import _ClientCheckout
 
+        class _BrokenSetupCheckout(_ClientCheckout):
+            def contribute_socket(self, conn, completed_handshake=True):
+                raise RuntimeError("simulated failure in post-checkout setup")
+
         client = self.rs_or_single_client()
         server = (client._get_topology()).select_server(writable_server_selector, _Op.TEST)
         pool = server.pool
 
-        checkout = _ClientCheckout(client, server, None)
-        with patch.object(checkout, "contribute_socket", side_effect=RuntimeError("simulated")):
-            with self.assertRaises(RuntimeError):
-                with checkout:
-                    pass
+        with self.assertRaises(RuntimeError):
+            with _BrokenSetupCheckout(client, server, None):
+                pass
 
         # Connection was returned to pool, not leaked.
         self.assertEqual(0, pool.active_sockets)