diff --git a/test/unit/mock/fake_account_client.py b/test/unit/mock/fake_account_client.py
index e08fb6eab..b11c8341b 100644
--- a/test/unit/mock/fake_account_client.py
+++ b/test/unit/mock/fake_account_client.py
@@ -76,6 +76,7 @@ def backend_configuration(self, backend_name: str) -> Dict[str, Any]:
         for backend in self._backends:
             if backend.name == backend_name:
                 return backend.configuration.copy()
+        raise ValueError(f"Backend {backend_name} not found")
 
     def backend_status(self, backend_name: str) -> Dict[str, Any]:
         """Return the status of the backend."""