add async test

(cherry picked from commit ebf65519f12d160da6d2088c22f6c69fad5a37d0)

Author: blink1073

test/test_client_backpressure.py

@@ -0,0 +1,57 @@
+# Copyright 2025-present MongoDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path[0:0] = [""]
+
+from test import (
+    IntegrationTest,
+    client_context,
+    unittest,
+)
+from test.unified_format import generate_test_classes
+from test.utils_shared import EventListener, OvertCommandListener
+
+_IS_SYNC = True
+
+
+class TestClientBackpressure(IntegrationTest):
+    listener: EventListener
+
+    @classmethod
+    def setUpClass(cls) -> None:
+        cls.listener = OvertCommandListener()
+
+    @client_context.require_connection
+    def setUp(self) -> None:
+        super().setUp()
+        self.listener.reset()
+        self.client = self.rs_or_single_client(event_listeners=[self.listener], retryWrites=False)
+
+
+_TEST_PATH = os.path.join(os.path.dirname(os.path.realpath(__file__)), "client-backpressure")
+
+
+globals().update(
+    generate_test_classes(
+        _TEST_PATH,
+        module=__name__,
+    )
+)
+
+if __name__ == "__main__":
+    unittest.main()