Remove GenericAPIView subclass from grades API views; add a test that /api-docs/ works.

lms/tests.py

@@ -3,8 +3,9 @@
 import logging
 import mimetypes
 
-from django.urls import reverse
+from django.conf import settings
 from django.test import TestCase
+from django.urls import reverse
 from mock import patch
 from six import text_type
 
@@ -29,6 +30,14 @@ class LmsModuleTests(TestCase):
             mimetype, _ = mimetypes.guess_type('test.' + extension)
             self.assertIsNotNone(mimetype)
 
+    def test_api_docs(self):
+        """
+        Tests that requests to the `/api-docs/` endpoint do not raise an exception.
+        """
+        assert settings.FEATURES['ENABLE_API_DOCS']
+        response = self.client.get('/api-docs/')
+        self.assertEqual(200, response.status_code)
+
 
 class TemplateLookupTests(TestCase):
     """