Sorted imports per isort 4.2.9.

tests/base/models.py

@@ -1,6 +1,5 @@
 from django.db import models
 
-
 # The models definitions below used to crash. Generating models dynamically
 # at runtime is a bad idea because it pollutes the app registry. This doesn't
 # integrate well with the test suite but at least it prevents regressions.