diff --git a/tests/unit/test_dedup_engine.py b/tests/unit/test_dedup_engine.py
index 2b8b2a656..a716c7ff9 100644
--- a/tests/unit/test_dedup_engine.py
+++ b/tests/unit/test_dedup_engine.py
@@ -42,8 +42,9 @@ _mock_if_absent("celery", MagicMock())
 if "celery" in sys.modules and isinstance(sys.modules["celery"], MagicMock):
     sys.modules["celery"].Task = object
 
-# Mock packages.shared.storage
-_mock_if_absent("packages.shared")
+# Mock packages.shared.storage（只 mock 目标子模块，不要 mock 父包
+# packages.shared——否则同进程后续从 packages.shared.* 导入任何子模块都会
+# 拿到 MagicMock，污染其他测试文件，例如 thumbnail_generator 的纯逻辑测试）
 _mock_if_absent("packages.shared.storage")
 
 # Mock packages.adapters.sqlalchemy_impl.generated_video_repository