implement handshake prose test

Author: blink1073

pymongo/asynchronous/pool.py

@@ -269,6 +269,7 @@ async def _hello(
         cmd = self.hello_cmd()
         performing_handshake = not self.performed_handshake
         awaitable = False
+        cmd["backpressure"] = True
         if performing_handshake:
             self.performed_handshake = True
             cmd["client"] = self.opts.metadata

pymongo/synchronous/pool.py

@@ -269,6 +269,7 @@ def _hello(
         cmd = self.hello_cmd()
         performing_handshake = not self.performed_handshake
         awaitable = False
+        cmd["backpressure"] = True
         if performing_handshake:
             self.performed_handshake = True
             cmd["client"] = self.opts.metadata

test/asynchronous/test_client_metadata.py

@@ -227,6 +227,19 @@ async def test_duplicate_driver_name_no_op(self):
         # add same metadata again
         await self.check_metadata_added(client, "Framework", None, None)
 
+    async def test_handshake_documents_include_backpressure(self):
+        # Create a `MongoClient` that is configured to record all handshake documents sent to the server as a part of
+        # connection establishment.
+        client = await self.async_rs_or_single_client("mongodb://" + self.server.address_string)
+
+        # Send a `ping` command to the server and verify that the command succeeds. This ensure that a connection is
+        # established on all topologies.  Note: MockupDB only supports standalone servers.
+        await client.admin.command("ping")
+
+        # Assert that for every handshake document intercepted:
+        # the document has a field `backpressure` whose value is `true`.
+        self.assertEqual(self.handshake_req["backpressure"], True)
+
 
 if __name__ == "__main__":
     unittest.main()

test/test_client_metadata.py

@@ -227,6 +227,19 @@ def test_duplicate_driver_name_no_op(self):
         # add same metadata again
         self.check_metadata_added(client, "Framework", None, None)
 
+    def test_handshake_documents_include_backpressure(self):
+        # Create a `MongoClient` that is configured to record all handshake documents sent to the server as a part of
+        # connection establishment.
+        client = self.rs_or_single_client("mongodb://" + self.server.address_string)
+
+        # Send a `ping` command to the server and verify that the command succeeds. This ensure that a connection is
+        # established on all topologies.  Note: MockupDB only supports standalone servers.
+        client.admin.command("ping")
+
+        # Assert that for every handshake document intercepted:
+        # the document has a field `backpressure` whose value is `true`.
+        self.assertEqual(self.handshake_req["backpressure"], True)
+
 
 if __name__ == "__main__":
     unittest.main()