use verbose_name instead of object_name in field_mapping (#4299)

* use verbose_name instead of object_name in error messages

rest_framework/utils/field_mapping.py

@@ -220,7 +220,7 @@ def get_field_kwargs(field_name, model_field):
         unique_error_message = model_field.error_messages.get('unique', None)
         if unique_error_message:
             unique_error_message = unique_error_message % {
-                'model_name': model_field.model._meta.object_name,
+                'model_name': model_field.model._meta.verbose_name,
                 'field_label': model_field.verbose_name
             }
         validator = UniqueValidator(

tests/test_validators.py

@@ -77,7 +77,7 @@ class TestUniquenessValidation(TestCase):
         data = {'username': 'existing'}
         serializer = UniquenessSerializer(data=data)
         assert not serializer.is_valid()
-        assert serializer.errors == {'username': ['UniquenessModel with this username already exists.']}
+        assert serializer.errors == {'username': ['uniqueness model with this username already exists.']}
 
     def test_is_unique(self):
         data = {'username': 'other'}