test_json: added Comment

Author: VanshAgarwal24036

Lib/test/test_json/test_fail.py

@@ -254,6 +254,10 @@ def __call__(self, *args, **kwargs):
         orig_decoder_error = json.decoder.JSONDecodeError
 
         try:
+            # NOTE: Do not use swap_attr() here.
+            # swap_attr() keeps the replacement object alive for the duration of
+            # the context manager, which prevents the crash this test is meant
+            # to reproduce
             json.JSONDecodeError = hook
             json.decoder.JSONDecodeError = hook
             del hook