[PATCH] kunit: tool: suppress confusing error output in test

[Jinseok Kim <always.starving0@gmail.com>]

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@gmail.com>
---
 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