diff --git a/bec_lib/bec_lib/tests/utils.py b/bec_lib/bec_lib/tests/utils.py
index bb0b2117..504336f4 100644
--- a/bec_lib/bec_lib/tests/utils.py
+++ b/bec_lib/bec_lib/tests/utils.py
@@ -1,16 +1,17 @@
 from __future__ import annotations
 
 import builtins
+import copy
+import functools
 import os
 import time
 import uuid
 from typing import TYPE_CHECKING
 from unittest import mock
 
+import bec_lib
 import pytest
 import yaml
-
-import bec_lib
 from bec_lib import BECClient, messages
 from bec_lib.connector import ConnectorBase
 from bec_lib.devicemanager import DeviceManagerBase
@@ -40,10 +41,15 @@ def dm():
     yield dev_manager
 
 
+@functools.lru_cache
+def load_test_config():
+    with open(f"{dir_path}/tests/test_config.yaml", "r", encoding="utf-8") as f:
+        return create_session_from_config(yaml.safe_load(f))
+
+
 @pytest.fixture
 def dm_with_devices(dm):
-    with open(f"{dir_path}/tests/test_config.yaml", "r") as f:
-        dm._session = create_session_from_config(yaml.safe_load(f))
+    dm._session = copy.deepcopy(load_test_config())
     dm._load_session()
     yield dm
 
diff --git a/device_server/tests/test_config_handler.py b/device_server/tests/test_config_handler.py
index d73a200c..7493fe5b 100644
--- a/device_server/tests/test_config_handler.py
+++ b/device_server/tests/test_config_handler.py
@@ -1,3 +1,4 @@
+import copy
 import os
 from unittest import mock
 
@@ -5,7 +6,7 @@ import bec_lib
 import pytest
 import yaml
 from bec_lib import messages
-from bec_lib.tests.utils import ConnectorMock, create_session_from_config
+from bec_lib.tests.utils import ConnectorMock, create_session_from_config, load_test_config
 from test_device_manager_ds import device_manager
 
 from device_server.devices.config_update_handler import ConfigUpdateHandler
@@ -20,8 +21,7 @@ def test_request_response():
     device_manager = DeviceManagerDS(service_mock)
 
     def get_config_from_mock():
-        with open(f"{dir_path}/tests/test_config.yaml", "r") as session_file:
-            device_manager._session = create_session_from_config(yaml.safe_load(session_file))
+        device_manager._session = copy.deepcopy(load_test_config())
         device_manager._load_session()
 
     def mocked_failed_connection(obj):
diff --git a/device_server/tests/test_device_manager_ds.py b/device_server/tests/test_device_manager_ds.py
index f72f2fc0..10cc0ff4 100644
--- a/device_server/tests/test_device_manager_ds.py
+++ b/device_server/tests/test_device_manager_ds.py
@@ -1,3 +1,5 @@
+import copy
+import functools
 import os
 from unittest import mock
 
@@ -48,14 +50,19 @@ class EpicsDeviceMock(DeviceMock):
         self._connected = True
 
 
+@functools.lru_cache()
+def load_test_config():
+    with open(f"{dir_path}/tests/test_config.yaml", "r", encoding="utf-8") as session_file:
+        return create_session_from_config(yaml.safe_load(session_file))
+
+
 def load_device_manager():
     service_mock = mock.MagicMock()
     service_mock.connector = ConnectorMock("", store_data=False)
     device_manager = DeviceManagerDS(service_mock, "")
     device_manager.connector = service_mock.connector
     device_manager.config_update_handler = mock.MagicMock()
-    with open(f"{dir_path}/tests/test_config.yaml", "r") as session_file:
-        device_manager._session = create_session_from_config(yaml.safe_load(session_file))
+    device_manager._session = copy.deepcopy(load_test_config())
     device_manager._load_session()
     return device_manager
 
@@ -101,8 +108,7 @@ def test_disable_unreachable_devices():
     device_manager = DeviceManagerDS(service_mock)
 
     def get_config_from_mock():
-        with open(f"{dir_path}/tests/test_config.yaml", "r") as session_file:
-            device_manager._session = create_session_from_config(yaml.safe_load(session_file))
+        device_manager._session = copy.deepcopy(load_test_config())
         device_manager._load_session()
 
     def mocked_failed_connection(obj):