diff --git a/tests/drawdag.py b/tests/drawdag.py
--- a/tests/drawdag.py
+++ b/tests/drawdag.py
@@ -214,6 +214,9 @@ class simplefilectx(object):
     def data(self):
         return self._data
 
+    def filenode(self):
+        return None
+
     def path(self):
         return self._path