update comment

Author: parthea

packages/gapic-generator/tests/system/test_resumable_upload_progress.py

@@ -257,7 +257,10 @@ def test_standalone_finalize_unseekable_stream(intercepted_resumable_upload_rest
 
 
 def test_client_upload_media_passes_request_body(intercepted_resumable_upload_rest):
-    """End-to-end test invoking client.upload_media(request=...) and verifying request body is sent on start."""
+    """ Verify that invoking `client.upload_media(request=UploadMediaRequest(...))`
+    and calling `session.upload(stream=...)` forwards the serialized request body
+    on the initial upload session start request so the server echoes back the
+    expected resource name in `UploadMediaResponse.name`."""
     client, _ = intercepted_resumable_upload_rest
     payload = b"0123456789" * 100
     stream = io.BytesIO(payload)