Add CLI argument to list tests and exit.

Example output (current dir is build directory under root dir):

  $ export PYTHONPATH=../python:../tests/functional
  $ export QEMU_TEST_QEMU_BINARY="$(pwd)/qemu-system-aarch64"
  $ ./pyvenv/bin/python3 ../tests/functional/test_aarch64_virt.py --list-tests
  test_aarch64_virt_gicv2 (test_aarch64_virt.Aarch64VirtMachine.test_aarch64_virt_gicv2)
  test_aarch64_virt_gicv3 (test_aarch64_virt.Aarch64VirtMachine.test_aarch64_virt_gicv3)
  test_alpine_virt_tcg_gic_max (test_aarch64_virt.Aarch64VirtMachine.test_alpine_virt_tcg_gic_max)

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
---
 tests/functional/qemu_test/testcase.py | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/tests/functional/qemu_test/testcase.py b/tests/functional/qemu_test/testcase.py
index 24f0b452964012532530a92018b2c4367b39fb77..4455fcc38016c14db04019bbd64eaae9b47363c1 100644
--- a/tests/functional/qemu_test/testcase.py
+++ b/tests/functional/qemu_test/testcase.py
@@ -50,6 +50,11 @@ def parse_args(test_name: str) -> argparse.Namespace:
         "This is equivalent to setting QEMU_TEST_KEEP_SCRATCH=1 in the "
         "environment.",
     )
+    parser.add_argument(
+        "--list-tests",
+        action="store_true",
+        help="List all tests that would be executed and exit.",
+    )
     return parser.parse_args()
 
 
@@ -281,10 +286,13 @@ def tearDown(self):
 
     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)
+        args = parse_args(path)
+        if args.list_tests:
+            loader = unittest.TestLoader()
+            for test_suite in loader.loadTestsFromName(path):
+                for test in test_suite:
+                    print(test)
+            return
 
         cache = os.environ.get("QEMU_TEST_PRECACHE", None)
         if cache is not None:

-- 
2.47.2