tests: add tests for non-existant branch/tag/bookmark

tests/test-bookmarks.t

@@ -84,6 +84,10 b' bookmarks revset'
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     1
   
+  $ hg log -r 'bookmark(unknown)'
+  abort: bookmark 'unknown' does not exist
+  [255]
+
   $ hg help revsets | grep 'bookmark('
       "bookmark([name])"
 

tests/test-revset.t

@@ -297,6 +297,12 b' quoting needed'
   6
   $ log 'tag(tip)'
   9
+  $ log 'tag(unknown)'
+  abort: tag 'unknown' does not exist
+  [255]
+  $ log 'branch(unknown)'
+  abort: unknown revision 'unknown'!
+  [255]
   $ log 'user(bob)'
   2