I am using Django 1.3.1. I have two databases, some of my models live in one database, some in the other. Both databases are contrib.gis.db.backends.postgis databases.
Note that multi_db is deprecated since Django 2.2. The new option to use is databases.
multi_db
Try this:
class MyTestCase(TestCase): multi_db = True
https://docs.djangoproject.com/en/1.2/topics/testing/#django.test.TestCase.multi_db