tests: demonstrate broken pull of "ffffffffffff" revision

Differential Revision: https://phab.mercurial-scm.org/D6214

tests/test-pull.t

@@ -75,6 +75,13 b' not are encoded like a node:'
   abort: unknown revision 'xxxxxxxxxxxxxxxxxx y'!
   [255]
 
+Test pull of working copy revision
+BROKEN: should give a better error message
+  $ hg pull -r 'ffffffffffff'
+  pulling from http://foo@localhost:$HGPORT/
+  abort: b2a_hex() argument 1 must be string or buffer, not None!
+  [255]
+
 Issue622: hg init && hg pull -u URL doesn't checkout default branch
 
   $ cd ..