--- a/tests/test-fold.t	Sun Jul 23 19:45:28 2017 +0200
+++ b/tests/test-fold.t	Mon Jul 24 01:45:03 2017 +0200
@@ -42,6 +42,10 @@
 
 Test various error case
 
+  $ hg fold --exact null::
+  abort: cannot fold the null revision
+  (no changeset checked out)
+  [255]
   $ hg fold
   abort: no revisions specified
   [255]