test: Verify loading from shelf files raises an AttributeError

This confirms @harriv's finding in #1313.

tests/test_sync.py

@@ -187,6 +187,15 @@ def test_sync_server_get_node(server, idx):
     assert vars[0].read_value() == 6.7
 
 
+@pytest.mark.xfail(
+        raises=AttributeError, reason="asyncua introduced a regression, likely when we switched to pathlib", strict=True
+    )
+async def test_sync_server_creating_shelf_files_works(tloop: ThreadLoop, tmp_path: Path) -> None:
+    shelf_file_path: Path = tmp_path / "shelf_file"
+
+    Server(tloop=tloop, shelf_file=shelf_file_path)
+
+
 class MySubHandler:
 
     def __init__(self):