diff --git a/tests/functional/pyocf/types/cache.py b/tests/functional/pyocf/types/cache.py
index 1b9863e..dfa5ea6 100644
--- a/tests/functional/pyocf/types/cache.py
+++ b/tests/functional/pyocf/types/cache.py
@@ -570,7 +570,7 @@ class Cache:
     def write_unlock(self):
         self.owner.lib.ocf_mngt_cache_unlock(self.cache_handle)
 
-    def add_core(self, core: Core):
+    def add_core(self, core: Core, try_add=False):
         self.write_lock()
 
         c = OcfCompletion(
@@ -582,8 +582,11 @@ class Cache:
             ]
         )
 
+        cfg = core.get_cfg()
+        cfg._try_add = try_add
+
         self.owner.lib.ocf_mngt_cache_add_core(
-            self.cache_handle, byref(core.get_cfg()), c, None
+            self.cache_handle, byref(cfg), c, None
         )
 
         c.wait()
diff --git a/tests/functional/pyocf/types/core.py b/tests/functional/pyocf/types/core.py
index 9e1f663..a862d7c 100644
--- a/tests/functional/pyocf/types/core.py
+++ b/tests/functional/pyocf/types/core.py
@@ -19,6 +19,9 @@ from ctypes import (
     cast,
     byref,
     create_string_buffer,
+    sizeof,
+    memmove,
+    pointer,
 )
 from datetime import timedelta
 
@@ -90,7 +93,10 @@ class Core:
         return c
 
     def get_cfg(self):
-        return self.cfg
+        config_copy = CoreConfig()
+        memmove(pointer(config_copy), pointer(self.cfg), sizeof(config_copy))
+
+        return config_copy
 
     def get_handle(self):
         return self.handle