nixos-test-driver: reintroduce --test-script flag (#533988)

nixos/lib/test-driver/src/test_driver/__init__.py

@@ -89,6 +89,11 @@ def main() -> None:
         type=Path,
         required=True,
     )
+    arg_parser.add_argument(
+        "--test-script",
+        help="path to a test script to run, taking precedence over the one defined in the config file",
+        type=Path,
+    )
     arg_parser.add_argument(
         "--keep-vm-state",
         help=argparse.SUPPRESS,
@@ -163,8 +168,12 @@ def main() -> None:
     if args.debug_hook_attach is not None:
         debugger = Debug(logger, args.debug_hook_attach)
 
+    config = load_driver_configuration(args.config)
+    if args.test_script is not None:
+        config.test_script = args.test_script
+
     with Driver(
-        config=load_driver_configuration(args.config),
+        config=config,
         out_dir=output_directory,
         logger=logger,
         keep_machine_state=args.keep_machine_state,