--- a/cubicweb/devtools/testlib.py	Wed Nov 23 18:38:46 2016 +0100
+++ b/cubicweb/devtools/testlib.py	Wed Nov 23 17:25:31 2016 +0100
@@ -1289,7 +1289,7 @@
                 self._test_action(action)
         for box in self.list_boxes_for(rset):
             w = [].append
-            with self.subTest(self._testname(rset, box.__regid__, 'box')):
+            with self.subTest(name=self._testname(rset, box.__regid__, 'box')):
                 box.render(w)
 
     @staticmethod