Make TestAcceptSubscription work..

..by using Django default test client instead of the one from
`rest_framework`.

djangoldp_webpushnotification/tests/tests_accept_subscription.py

@@ -1,17 +1,15 @@
 import json
 
 from django.contrib.auth import get_user_model
-from django.test import TestCase
 from django.urls import reverse
-from rest_framework.test import APIClient, APIRequestFactory, APITestCase
+from django.test import Client, TestCase
 
 
 class TestAcceptSubscription(TestCase):
     def setUp(self):
-        self.factory = APIRequestFactory()
-        self.client = APIClient()
-        self.user = get_user_model().objects.create_user(username='john', email='jlennon@beatles.com', password='glass onion')
-        self.client.force_authenticate(self.user)
+        self.client = Client()
+        self.user = get_user_model().objects.create(username='john', email='jlennon@beatles.com', password='glass onion')
+        self.client.force_login(self.user)
 
     def tearDown(self):
         self.user.delete()