Use assert when checking for reserved field names (#1025)

This check is for development purposes to verify that the source code
is well configured but not needed during production. Therefore a assert
is more appropriate.

Author: sliverc

rest_framework_json_api/serializers.py

@@ -165,12 +165,11 @@ def get_fields(self):
         found_reserved_field_names = self._reserved_field_names.intersection(
             fields.keys()
         )
-        if found_reserved_field_names:
-            raise AttributeError(
-                f"Serializer class {self.__class__.__module__}.{self.__class__.__qualname__} "
-                f"uses following reserved field name(s) which is not allowed: "
-                f"{', '.join(sorted(found_reserved_field_names))}"
-            )
+        assert not found_reserved_field_names, (
+            f"Serializer class {self.__class__.__module__}.{self.__class__.__qualname__} "
+            f"uses following reserved field name(s) which is not allowed: "
+            f"{', '.join(sorted(found_reserved_field_names))}"
+        )
 
         if "type" in fields:
             # see https://jsonapi.org/format/#document-resource-object-fields

tests/test_serializers.py

@@ -37,7 +37,7 @@ class Meta:
 
 
 def test_reserved_field_names():
-    with pytest.raises(AttributeError) as e:
+    with pytest.raises(AssertionError) as e:
 
         class ReservedFieldNamesSerializer(serializers.Serializer):
             meta = serializers.CharField()