Check for osmo_fsm_register() error return value

Change-Id: Idbc1557739b2a253b73914e6f1f18a6d169d882e
diff --git a/tests/fsm/fsm_test.c b/tests/fsm/fsm_test.c
index f8ebdc7..911aad8 100644
--- a/tests/fsm/fsm_test.c
+++ b/tests/fsm/fsm_test.c
@@ -417,7 +417,7 @@
 
 	g_ctx = NULL;
 	OSMO_ASSERT(osmo_fsm_find_by_name(fsm.name) == NULL);
-	osmo_fsm_register(&fsm);
+	OSMO_ASSERT(osmo_fsm_register(&fsm) == 0);
 	OSMO_ASSERT(osmo_fsm_find_by_name(fsm.name) == &fsm);
 
 	OSMO_ASSERT(osmo_fsm_inst_find_by_name(&fsm, "my_id") == NULL);