Test a logout scenario in Google App Engine and webtest

Question

I'm having a hard time making this simple test work:

class TestNotlogedUser(unittest.TestCase):
    def setUp(self):
        unittest.TestCase.setUp(self)
        self.testapp = webtest.TestApp(application)
        self.testbed = testbed.Testbed()
        self.testbed.activate()
        self.testbed.init_datastore_v3_stub()
        self.testbed.init_user_stub()

    def tearDown(self):
        self.testbed.deactivate()

    def test_user_profile_301(self):
        resp = self.testapp.get('/profile/logout/')
        resp.click(linkid='logout') # user logs out
        resp = self.testapp.get('/profile/')
        self.assertEquals(resp.status_int, 301, resp) # user is redirected to a login page

But it throws this error:

AppError: Bad response: 404 NOT FOUND (not 200 OK or 3xx redirect for http://localhost/accounts/Logout?continue=http%3A//testbed.example.com/)

This part is the one causing trouble continue=http%3A//testbed.example.com, I want to change the host to localhost:8080.

Acording to the github source you pass an extra_environ to the constructor:

:param extra_environ:
        A dictionary of values that should go
        into the environment for each request. These can provide a
        communication channel with the application.

My question is it is possible to change the testbed.example.com as a value of this parameter, I'm still loking at source but it seems there's not documentation for the name of the keys of this extra_environ dictionary.