bpo-40528: Improve and clear several aspects of the ASDL definition code for the AST (GH-19952)

diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index a8a13fd..6b71ada 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -597,7 +597,7 @@
         empty_yield_from.body[0].body[0].value.value = None
         with self.assertRaises(ValueError) as cm:
             compile(empty_yield_from, "<test>", "exec")
-        self.assertIn("field value is required", str(cm.exception))
+        self.assertIn("field 'value' is required", str(cm.exception))
 
     @support.cpython_only
     def test_issue31592(self):