tests: show poor error message for `hg cp -A --at-rev . non-existent dst` stable

tests: show poor error message for  `hg cp -A --at-rev . non-existent dst`

Differential Revision: https://phab.mercurial-scm.org/D8495

--- a/tests/test-rename-rev.t	Wed May 06 10:33:56 2020 -0700
+++ b/tests/test-rename-rev.t	Wed May 06 11:41:37 2020 -0700
@@ -11,7 +11,7 @@
 
 Test single file
 
-# One recoded copy, one copy to record after commit
+# One recorded copy, one copy to record after commit
   $ hg cp d1/b d1/c
   $ cp d1/b d1/d
   $ hg add d1/d
@@ -24,6 +24,12 @@
   $ hg cp --at-rev . d1/b d1/d
   abort: --at-rev requires --after
   [255]
+# Errors out with non-existent source
+BROKEN: this should have a better error message
+  $ hg cp -A --at-rev . d1/non-existent d1/d
+  d1/non-existent: no such file in rev 55d1fd85ef0a
+  abort: --at-rev requires a single source
+  [255]
 # Errors out with non-existent destination
   $ hg cp -A --at-rev . d1/b d1/non-existent
   abort: d1/non-existent: copy destination does not exist in 8a9d70fa20c9