gh-125542: Deprecate prefix_chars in ArgumentParser.add_argument_group() (GH-125563)

1 files changed, 25 insertions, 0 deletions

diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index a3c096e..4fa6697 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2893,6 +2893,31 @@ class TestPositionalsGroups(TestCase):
         result = parser.parse_args('1 2 3 4'.split())
         self.assertEqual(expected, result)
 
+class TestGroupConstructor(TestCase):
+    def test_group_prefix_chars(self):
+        parser = ErrorRaisingArgumentParser()
+        msg = (
+            "The use of the undocumented 'prefix_chars' parameter in "
+            "ArgumentParser.add_argument_group() is deprecated."
+        )
+        with self.assertWarns(DeprecationWarning) as cm:
+            parser.add_argument_group(prefix_chars='-+')
+        self.assertEqual(msg, str(cm.warning))
+        self.assertEqual(cm.filename, __file__)
+
+    def test_group_prefix_chars_default(self):
+        # "default" isn't quite the right word here, but it's the same as
+        # the parser's default prefix so it's a good test
+        parser = ErrorRaisingArgumentParser()
+        msg = (
+            "The use of the undocumented 'prefix_chars' parameter in "
+            "ArgumentParser.add_argument_group() is deprecated."
+        )
+        with self.assertWarns(DeprecationWarning) as cm:
+            parser.add_argument_group(prefix_chars='-')
+        self.assertEqual(msg, str(cm.warning))
+        self.assertEqual(cm.filename, __file__)
+
 # ===================
 # Parent parser tests
 # ===================