Raise ImproperlyConfigured when missing serializer_class

get_serializer_class raises an AssertionError if no serializer_class
is found (either as a class attribute or from an overriding method).
This commit catches it and raises ImproperlyConfigured instead.

rest_framework/filters.py

@@ -227,14 +227,14 @@ class OrderingFilter(BaseFilterBackend):
 
         if valid_fields is None:
             # Default to allowing filtering on serializer fields
-            serializer_class = getattr(view, 'serializer_class')
-            if serializer_class is None:
+            try:
                 serializer_class = view.get_serializer_class()
-                if serializer_class is None:
-                    msg = ("Cannot use %s on a view which does not have either a "
-                           "'serializer_class', an overriding 'get_serializer_class' "
-                           "or 'ordering_fields' attribute.")
-                    raise ImproperlyConfigured(msg % self.__class__.__name__)
+            except AssertionError:  # raised if no serializer_class was found
+                msg = ("Cannot use %s on a view which does not have either a "
+                       "'serializer_class', an overriding 'get_serializer_class' "
+                       "or 'ordering_fields' attribute.")
+                raise ImproperlyConfigured(msg % self.__class__.__name__)
+
             valid_fields = [
                 (field.source or field_name, field.label)
                 for field_name, field in serializer_class().fields.items()

tests/test_filters.py

@@ -5,6 +5,7 @@ import unittest
 from decimal import Decimal
 
 from django.conf.urls import url
+from django.core.exceptions import ImproperlyConfigured
 from django.core.urlresolvers import reverse
 from django.db import models
 from django.test import TestCase
@@ -786,8 +787,7 @@ class OrderingFilterTests(TestCase):
 
         view = OrderingListView.as_view()
         request = factory.get('/', {'ordering': 'text'})
-        # BUG: I think this should raise ImproperlyConfigured
-        with self.assertRaises(AssertionError):
+        with self.assertRaises(ImproperlyConfigured):
             view(request)