--- a/mercurial/vfs.py	Wed Jan 02 10:29:36 2019 +0100
+++ b/mercurial/vfs.py	Wed Jan 02 10:31:14 2019 +0100
@@ -47,7 +47,7 @@
         raise NotImplementedError('attempted instantiating ' + str(type(self)))
 
     def _auditpath(self, path, mode):
-        pass
+        raise NotImplementedError
 
     def tryread(self, path):
         '''gracefully return an empty string for missing files'''