Code review comment for lp://staging/~zsombi/ubuntu-ui-toolkit/70-cpos

Looks pretty good. Just, please change the last two tests to something like this:

def test_trigger_nonexistent_leading_action(self):
    error = self.assertRaises(
       ubuntuuitoolkit.ToolkitException,
       self.test_listitem.trigger_leading_action,
       'this_action_does_not_exist')
    self.assertEqual(
        str(error),
       'The requested action not found on leading side')