Slightly nicer error message for not.

Author: Julian

jsonschema/_validators.py

@@ -397,9 +397,8 @@ def oneOf(validator, oneOf, instance, schema):
 
 def not_(validator, not_schema, instance, schema):
     if validator.is_valid(instance, not_schema):
-        yield ValidationError(
-            f"{not_schema!r} is not allowed for {instance!r}",
-        )
+        message = f"{instance!r} should not be valid under {not_schema!r}"
+        yield ValidationError(message)
 
 
 def if_(validator, if_schema, instance, schema):

jsonschema/tests/test_validators.py

@@ -1022,7 +1022,7 @@ def test_propertyNames(self):
         self.assertEqual(error.validator, "not")
         self.assertEqual(
             error.message,
-            "{'const': 'foo'} is not allowed for 'foo'",
+            "'foo' should not be valid under {'const': 'foo'}",
         )
         self.assertEqual(error.path, deque([]))
         self.assertEqual(error.json_path, "$")