diff --git a/swh/storage/tests/test_storage.py b/swh/storage/tests/test_storage.py
--- a/swh/storage/tests/test_storage.py
+++ b/swh/storage/tests/test_storage.py
@@ -180,6 +180,8 @@
         cont = data.cont
 
         class LazyContent(Content):
+            __type__ = 'Content'
+
             def with_data(self):
                 nonlocal called
                 called = True