tests: add tests for rebasing wdir() revision

Differential Revision: https://phab.mercurial-scm.org/D8056

tests/test-rebase-parameters.t

@@ -92,6 +92,13 b' These fail:'
   empty "rev" revision set - nothing to rebase
   [1]
 
+  $ hg rebase --rev 'wdir()' --dest 6
+  abort: working directory revision cannot be specified
+  [255]
+
+  $ hg rebase --source 'wdir()' --dest 6 2>&1 | grep assert
+      assert rebaseset
+
   $ hg rebase --source '1 & !1' --dest 8
   empty "source" revision set - nothing to rebase
   [1]