diff --git a/tests/gateway/test_compression_failure_session_sync.py b/tests/gateway/test_compression_failure_session_sync.py
index 8874c016cce..d24021a0f03 100644
--- a/tests/gateway/test_compression_failure_session_sync.py
+++ b/tests/gateway/test_compression_failure_session_sync.py
@@ -21,10 +21,16 @@ class _SessionStore:
         )
         self._entries = {SESSION_KEY: self.entry}
         self.save_calls = 0
+        self.peer_records = []
 
     def _save(self):
         self.save_calls += 1
 
+    def _record_gateway_session_peer(self, session_id, session_key, source):
+        # #55300 records the child's gateway peer metadata after a compression
+        # split; the fake tracks the call so tests can assert it fired.
+        self.peer_records.append((session_id, session_key, source))
+
 
 class _CompressionThenFailureAgent:
     def __init__(self, **kwargs):