gh-103186: Fix or catch 'extra' stderr output from unittests (#103196)

Reduce test noise by fixing or catching and testing stderr messages from individual tests.

test_cmd_line_script.test_script_as_dev_fd calls spawn_python and hence subprocess.Popen with incompatible arguments. On POSIX, pass_fds forces close_fds to be True (subprocess.py line 848). Correct the call.

test_uuid.test_cli_namespace_required_for_uuid3: when the namespace is omitted, uuid.main calls argparse.Argument_Parser.error, which prints to stderr before calling sys.exit, which raises SystemExit. Unittest assertRaises catches the exception but not the previous output. Catch the output and test it.

test_warnings.test_catchwarnings_with_simplefilter_error similarly prints before raising. Catch the output and test it.
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Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/Lib/test/test_cmd_line_script.py b/Lib/test/test_cmd_line_script.py
index 8bf2993..1b58882 100644
--- a/Lib/test/test_cmd_line_script.py
+++ b/Lib/test/test_cmd_line_script.py
@@ -777,7 +777,7 @@ class CmdLineTest(unittest.TestCase):
         with os_helper.temp_dir() as work_dir:
             script_name = _make_test_script(work_dir, 'script.py', script)
             with open(script_name, "r") as fp:
-                p = spawn_python(f"/dev/fd/{fp.fileno()}", close_fds=False, pass_fds=(0,1,2,fp.fileno()))
+                p = spawn_python(f"/dev/fd/{fp.fileno()}", close_fds=True, pass_fds=(0,1,2,fp.fileno()))
                 out, err = p.communicate()
                 self.assertEqual(out, b"12345678912345678912345\n")