Add internal classes and add type hints + mypy.

tests/test_project/settings.py

@@ -10,11 +10,11 @@ For the full list of settings and their values, see
 https://docs.djangoproject.com/en/2.1/ref/settings/
 """
 
+from __future__ import annotations
+
 import os
 
 # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
-from collections import OrderedDict
-
 BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))