Added additional test for Cmd._build_parser().

Author: kmvanbrunt

CHANGELOG.md

@@ -1,8 +1,14 @@
 ## 2.6.2 (TBD, 2025)
 
 - Enhancements
+
     - Added explicit support for free-threaded versions of Python, starting with version 3.14
 
+- Bug Fixes
+    - Restored code to set a parser's `prog` value in the `with_argparser` decorator. This is to
+      preserve backward compatibility in the `cmd2` 2.0 family. This functionality will be removed
+      in `cmd2` 3.0.0.
+
 ## 2.6.1 (June 8, 2025)
 
 - Bug Fixes

cmd2/decorators.py

@@ -395,8 +395,10 @@ def cmd_wrapper(*args: Any, **kwargs: dict[str, Any]) -> Optional[bool]:
 
         if isinstance(parser, argparse.ArgumentParser):
             # Set parser's prog value for backward compatibility within the cmd2 2.0 family.
-            # This will be removed in cmd2 3.0 since we never reference this parser's prog value.
-            # We only set prog on the deep copy of this parser created in Cmd._build_parser().
+            # This will be removed in cmd2 3.0 since we never reference this parser object's prog value.
+            # Since it's possible for the same parser object to be passed into multiple with_argparser()
+            # calls, we only set prog on the deep copies of this parser based on the specific do_xxxx
+            # instance method they are associated with.
             _set_parser_prog(parser, command_name)
 
         # Set some custom attributes for this command

tests/test_argparse.py

@@ -248,6 +248,12 @@ def test_preservelist(argparse_app) -> None:
     assert out[0] == "['foo', '\"bar baz\"']"
 
 
+def test_invalid_parser_builder(argparse_app):
+    parser_builder = None
+    with pytest.raises(TypeError):
+        argparse_app._build_parser(argparse_app, parser_builder, "fake_prog")
+
+
 def _build_has_subcmd_parser() -> cmd2.Cmd2ArgumentParser:
     has_subcmds_parser = cmd2.Cmd2ArgumentParser(description="Tests as_subcmd_to decorator")
     has_subcmds_parser.add_subparsers(dest='subcommand', metavar='SUBCOMMAND', required=True)