Comment 2 for bug 259275

Here's a test case (which explodes in tree building, as mentioned):

    def test_push_doesnt_create_broken_branch(self):
        tree = self.make_branch_and_tree('a')
        self.build_tree(['a/file'])
        tree.add('file')
        tree.commit('commit')
        self.make_bzrdir('.').get_config().set_default_stack_on('a')
        self.run_bzr('push -d a b')

(I put it in TestPush in bzrlib.tests.blackbox.test_push.TestPush)