Add argument parsing to functional tests to improve developer experience
when running individual tests. All logs are printed to stdout
interspersed with TAP output.

Example usage, assuming current build directory with qemu source code in
the parent directory (see docs/devel/testing/functional.rst for details):

  $ export PYTHONPATH=../python:../tests/functional
  $ export QEMU_TEST_QEMU_BINARY="$(pwd)/qemu-system-aarch64"
  $ ./pyvenv/bin/python3 ../tests/functional/test_aarch64_virt.py --help
  usage: test_aarch64_virt [-h] [-d]

  QEMU Functional test

  options:
    -h, --help   show this help message and exit
    -d, --debug  Also print test and console logs on stdout. This will
                 make the TAP output invalid and is meant for debugging
                 only.

Signed-off-by: Manos Pitsidianakis <manos.pitsidiana...@linaro.org>
---
Changes in v2:
- Store stdout handler in `self` object (thanks Daniel)
- Deduplicate handler removal code (Daniel)
- Amend commit description to mention PYTHONPATH (thanks Alex)
- Link to v1: 
https://lore.kernel.org/qemu-devel/20250716-functional_tests_debug_arg-v1-1-6a9cd6831...@linaro.org
---
 docs/devel/testing/functional.rst      |  2 ++
 tests/functional/qemu_test/testcase.py | 48 +++++++++++++++++++++++++++++++---
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/docs/devel/testing/functional.rst 
b/docs/devel/testing/functional.rst
index 
9e56dd1b1189216b9b4aede00174c15203f38b41..9d08abe2848277d635befb0296f578cfaa4bd66d
 100644
--- a/docs/devel/testing/functional.rst
+++ b/docs/devel/testing/functional.rst
@@ -63,6 +63,8 @@ directory should be your build folder. For example::
   $ export QEMU_TEST_QEMU_BINARY=$PWD/qemu-system-x86_64
   $ pyvenv/bin/python3 ../tests/functional/test_file.py
 
+By default, functional tests redirect informational logs and console output to
+log files. Specify the ``--debug`` flag to also print those to standard output.
 The test framework will automatically purge any scratch files created during
 the tests. If needing to debug a failed test, it is possible to keep these
 files around on disk by setting ```QEMU_TEST_KEEP_SCRATCH=1``` as an env
diff --git a/tests/functional/qemu_test/testcase.py 
b/tests/functional/qemu_test/testcase.py
index 
2082c6fce43b0544d4e4258cd4155f555ed30cd4..3ecaaeffd4df2945fb4c44b4ddef6911527099b9
 100644
--- a/tests/functional/qemu_test/testcase.py
+++ b/tests/functional/qemu_test/testcase.py
@@ -11,6 +11,7 @@
 # This work is licensed under the terms of the GNU GPL, version 2 or
 # later.  See the COPYING file in the top-level directory.
 
+import argparse
 import logging
 import os
 from pathlib import Path
@@ -31,6 +32,20 @@
 from .uncompress import uncompress
 
 
+def parse_args(test_name: str) -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        prog=test_name, description="QEMU Functional test"
+    )
+    parser.add_argument(
+        "-d",
+        "--debug",
+        action="store_true",
+        help="Also print test and console logs on stdout. This will make the"
+        " TAP output invalid and is meant for debugging only.",
+    )
+    return parser.parse_args()
+
+
 class QemuBaseTest(unittest.TestCase):
 
     '''
@@ -196,6 +211,16 @@ def assets_available(self):
         return True
 
     def setUp(self):
+        path = os.path.basename(sys.argv[0])[:-3]
+        args = parse_args(path)
+        self.stdout_handler = None
+        if args.debug:
+            self.stdout_handler = logging.StreamHandler(sys.stdout)
+            self.stdout_handler.setLevel(logging.DEBUG)
+            formatter = logging.Formatter(
+                "%(asctime)s - %(name)s - %(levelname)s - %(message)s"
+            )
+            self.stdout_handler.setFormatter(formatter)
         self.qemu_bin = os.getenv('QEMU_TEST_QEMU_BINARY')
         self.assertIsNotNone(self.qemu_bin, 'QEMU_TEST_QEMU_BINARY must be 
set')
         self.arch = self.qemu_bin.split('-')[-1]
@@ -215,12 +240,17 @@ def setUp(self):
             '%(asctime)s - %(levelname)s: %(message)s')
         self._log_fh.setFormatter(fileFormatter)
         self.log.addHandler(self._log_fh)
+        if self.stdout_handler:
+            self.log.addHandler(self.stdout_handler)
 
         # Capture QEMUMachine logging
         self.machinelog = logging.getLogger('qemu.machine')
         self.machinelog.setLevel(logging.DEBUG)
         self.machinelog.addHandler(self._log_fh)
 
+        if self.stdout_handler:
+            self.machinelog.addHandler(self.stdout_handler)
+
         if not self.assets_available():
             self.skipTest('One or more assets is not available')
 
@@ -230,11 +260,18 @@ def tearDown(self):
         if self.socketdir is not None:
             shutil.rmtree(self.socketdir.name)
             self.socketdir = None
-        self.machinelog.removeHandler(self._log_fh)
-        self.log.removeHandler(self._log_fh)
+        for handler in [self._log_fh, self.stdout_handler]:
+            if handler is None:
+                continue
+            self.machinelog.removeHandler(handler)
+            self.log.removeHandler(handler)
 
     def main():
         path = os.path.basename(sys.argv[0])[:-3]
+        # If argparse receives --help or an unknown argument, it will raise a
+        # SystemExit which will get caught by the test runner. Parse the
+        # arguments here too to handle that case.
+        parse_args(path)
 
         cache = os.environ.get("QEMU_TEST_PRECACHE", None)
         if cache is not None:
@@ -292,6 +329,8 @@ def setUp(self):
         fileFormatter = logging.Formatter('%(asctime)s: %(message)s')
         self._console_log_fh.setFormatter(fileFormatter)
         console_log.addHandler(self._console_log_fh)
+        if self.stdout_handler:
+            console_log.addHandler(self.stdout_handler)
 
     def set_machine(self, machinename):
         # TODO: We should use QMP to get the list of available machines
@@ -398,5 +437,8 @@ def set_vm_arg(self, arg, value):
     def tearDown(self):
         for vm in self._vms.values():
             vm.shutdown()
-        logging.getLogger('console').removeHandler(self._console_log_fh)
+        console_log = logging.getLogger("console")
+        console_log.removeHandler(self._console_log_fh)
+        if self.stdout_handler:
+            console_log.removeHandler(self.stdout_handler)
         super().tearDown()

---
base-commit: f96b157ebb93f94cd56ebbc99bc20982b8fd86ef
change-id: 20250716-functional_tests_debug_arg-aa0a5f6b9375

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