This problems gave me great headache when i tried to use reverse for generating activation link and send it via email of course. So i think from tests.py it will be same. The correct way to do this is following:
from django.test import Client
from django.core.urlresolvers import reverse
#app name - name of the app where the url is defined
client= Client()
response = client.get(reverse('app_name:edit_project', project_id=4))