pw_transfer: Add transfer rate to integration test

Change-Id: Id6e8e060d22cfa950ac41383af5e5af6e9c9d41d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/91981
Reviewed-by: Ted Pudlik <tpudlik@google.com>
Commit-Queue: Erik Gilling <konkers@google.com>

pw_transfer/integration_test/cross_language_integration_test.py

@@ -26,6 +26,7 @@
 import random
 import sys
 import tempfile
+import time
 from typing import List
 import unittest
 
@@ -256,12 +257,18 @@ async def _perform_write(self, server_config: config_pb2.ServerConfig,
                 await self._server.wait_for_line(
                     "stderr", "Starting pw_rpc server on port", TIMEOUT)
 
+                start = time.monotonic()
+
                 await self._start_client(client_type, client_config)
                 # No timeout: the client will only exit once the transfer
                 # completes, and this can take a long time for large payloads.
                 await self._client.wait_for_termination(None)
                 self.assertEqual(self._client.returncode(), 0)
 
+                duration = time.monotonic() - start
+                rate = len(payload) / duration
+                print(f'Client transfer rate: {rate} B/s')
+
                 # Wait for the server to exit.
                 await self._server.wait_for_termination(TIMEOUT)
                 self.assertEqual(self._server.returncode(), 0)