linux-kernel - Re: [PATCH] kunit: tool: suppress confusing error output in test

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Message-ID: <CABVgOSmnqS5Qy=HVFTj_JivoBggKvw-iKaX==4C0SGLK82Tf6w@mail.gmail.com>
Date: Fri, 16 Jan 2026 17:30:19 +0800
From: David Gow <davidgow@...gle.com>
To: Jinseok Kim <always.starving0@...il.com>
Cc: brendan.higgins@...ux.dev, raemoar63@...il.com, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kunit: tool: suppress confusing error output in test

On Mon, 12 Jan 2026 at 12:14, Jinseok Kim <always.starving0@...il.com> wrote:
>
> When running kunit_tool_test.py, the test_run_raw_output_invalid test
> prints invalid usage text and error messages to stderr. This happens because the
> test triggers kunit.main() with an invalid argument, causing argparse to
> print the usage and exit.
>
> This output is confusing to the user because it looks like a test failure
> or usage error, even though the test passed successfully. Furthermore,
> argparse displays 'usage: kunit_tool_test.py run ...', which is misleading
> since the test script itself does not accept the 'run' command.
>
> This patch mocks sys.stderr in the test to suppress this expected error
> output, making the test execution output cleaner.
>
> Signed-off-by: Jinseok Kim <always.starving0@...il.com>
> ---

This has been slightly annoying for a long time, so thanks for fixing it.

One minor nitpick in the commit description, otherwise this is good:

WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit
description?)
#11:
prints invalid usage text and error messages to stderr. This happens because the

Reviewed-by: David Gow <davidgow@...gle.com>

Cheers,
-- David


>  tools/testing/kunit/kunit_tool_test.py | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/kunit/kunit_tool_test.py b/tools/testing/kunit/kunit_tool_test.py
> index bbba921e0eac..7a8ba8e4f1d4 100755
> --- a/tools/testing/kunit/kunit_tool_test.py
> +++ b/tools/testing/kunit/kunit_tool_test.py
> @@ -8,6 +8,7 @@
>
>  import unittest
>  from unittest import mock
> +import io
>
>  import tempfile, shutil # Handling test_tmpdir
>
> @@ -688,8 +689,9 @@ class KUnitMainTest(unittest.TestCase):
>
>         def test_run_raw_output_invalid(self):
>                 self.linux_source_mock.run_kernel = mock.Mock(return_value=[])
> -               with self.assertRaises(SystemExit) as e:
> -                       kunit.main(['run', '--raw_output=invalid'])
> +               with mock.patch('sys.stderr', new=io.StringIO()):
> +                       with self.assertRaises(SystemExit) as e:
> +                               kunit.main(['run', '--raw_output=invalid'])
>                 self.assertNotEqual(e.exception.code, 0)
>
>         def test_run_raw_output_does_not_take_positional_args(self):
> --
> 2.43.0

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