Error with urlresolvers.reverse when running tests for admin

[Derek]

I am struggling to get 'reverse' working when running tests for actions defined in my admin.py files.

If I open a Django shell and run:

from django.core.urlresolvers import reverse

print reverse('admin:trees_alivetrees_changelist')

I get:

/admin/trees/alivetrees/

as expected.

But if I define a test file (called `test_admin_fail.py`):

from django.test import TestCase

from django.core.urlresolvers import reverse

class TreeAdminTest(TestCase):

    def test_action_tree_mark_dead(self):

        change_url = reverse('admin:trees_alivetrees_changelist')

        self.assertContains(change_url, "alivetrees")   # temporary test

and run it from the command line:

python manage.py test --traverse-namespace tests.trees.test_admin_fail -v 2 --settings=test_settings

then I get this error:

Traceback (most recent call last):

  File "/dev/tests/trees/test_admin_fail.py", line 7, in test_action_tree_mark_dead

    change_url = reverse('admin:trees_alivetrees_changelist')

  File "/.virtualenvs/s2/local/lib/python2.7/site-packages/django/core/urlresolvers.py", line 536, in reverse

    return iri_to_uri(resolver._reverse_with_prefix(view, prefix, *args, **kwargs))

  File "/home/derek/.virtualenvs/s2/local/lib/python2.7/site-packages/django/core/urlresolvers.py", line 456, in _reverse_with_prefix

    (lookup_view_s, args, kwargs, len(patterns), patterns))

NoReverseMatch: Reverse for 'trees_alivetrees_changelist' with arguments '()' and keyword arguments '{}' not found. 0 pattern(s) tried: []

-------------------- >> begin captured stdout << ---------------------

nose.proxy:128 err (<class 'django.core.urlresolvers.NoReverseMatch'>, NoReverseMatch(u"Reverse for 'trees_alivetrees_changelist' with arguments '()' and keyword arguments '{}' not found. 0 pattern(s) tried: []",), <traceback object at 0x7fe779406c20>)

The test_settings.py file is used to create an in-memory database (and has never itself caused any issues before).

Any guidance here would be appreciated; I have tried Googling for the error, but the combination of admin, testing and reverse is one I have not seen.

Thanks

Derek