diff --git a/tests/test_four_phase_unit.py b/tests/test_four_phase_unit.py
index bba6fb8..9da7b70 100644
--- a/tests/test_four_phase_unit.py
+++ b/tests/test_four_phase_unit.py
@@ -211,6 +211,8 @@ class TestU3RoundComplete:
         mock_spawner.api_port = 8083
         ticker = Ticker(registry=ProjectRegistry(Path("/tmp/fake")),
                         spawner=mock_spawner, dispatcher=MagicMock())
+        # mock _build_review_prompt（f-string 在 Python 3.9 有兼容性问题）
+        ticker._build_review_prompt = MagicMock(return_value="Review prompt mock")
 
         async def run():
             result = await ticker._check_round_complete(db_path, pid)