Declare sample models for access_token, refresh_token and grant.

Author: Aristobulo Meneses

tests/models.py

@@ -1,7 +1,24 @@
 from django.db import models
 
-from oauth2_provider.models import AbstractApplication
+from oauth2_provider.models import (
+    AbstractApplication,
+    AbstractAccessToken,
+    AbstractGrant,
+    AbstractRefreshToken,
+)
 
 
 class SampleApplication(AbstractApplication):
     custom_field = models.CharField(max_length=255)
+
+
+class SampleAccessToken(AbstractAccessToken):
+    custom_field = models.CharField(max_length=255)
+
+
+class SampleRefreshToken(AbstractRefreshToken):
+    custom_field = models.CharField(max_length=255)
+
+
+class SampleGrant(AbstractGrant):
+    custom_field = models.CharField(max_length=255)