adds function testing if private attributes can take values that are not serializable

tests/data_service/test_data_service_observer.py

@@ -1,9 +1,11 @@
 import logging
+from typing import Any
 
 import pydase
 import pytest
 from pydase.data_service.data_service_observer import DataServiceObserver
 from pydase.data_service.state_manager import StateManager
+from pydase.utils.serialization.serializer import SerializationError
 
 logger = logging.getLogger()
 
@@ -122,3 +124,25 @@ def test_dynamic_list_entry_with_property(caplog: pytest.LogCaptureFixture) -> N
 
     assert "'list_attr[0].name' changed to 'Hello'" not in caplog.text
     assert "'list_attr[0].name' changed to 'Hoooo'" in caplog.text
+
+
+def test_private_attribute_does_not_have_to_be_serializable() -> None:
+    class MyService(pydase.DataService):
+        def __init__(self) -> None:
+            super().__init__()
+            self.publ_attr: Any = 1
+            self.__priv_attr = (1,)
+
+        def change_publ_attr(self) -> None:
+            self.publ_attr = (2,)  # cannot be serialized
+
+        def change_priv_attr(self) -> None:
+            self.__priv_attr = (2,)
+
+    service_instance = MyService()
+    pydase.Server(service_instance)
+
+    with pytest.raises(SerializationError):
+        service_instance.change_publ_attr()
+
+    service_instance.change_priv_attr()