tdef_test: verify case where osmo_tdef_set returns -EEXIST

Change-Id: I436daa804aac11622fde24afe9ea35193d9e9beb
diff --git a/tests/tdef/tdef_test.c b/tests/tdef/tdef_test.c
index 60066b1..276330a 100644
--- a/tests/tdef/tdef_test.c
+++ b/tests/tdef/tdef_test.c
@@ -179,6 +179,9 @@
 	print_tdef_get_short(tdefs, 7, OSMO_TDEF_M);
 	print_tdef_get_short(tdefs, 7, OSMO_TDEF_CUSTOM);
 
+	printf("setting 23 = 50 (EEXIST)\n");
+	OSMO_ASSERT(osmo_tdef_set(tdefs, 23, 50, OSMO_TDEF_S) == -EEXIST);
+
 	printf("resetting\n");
 	osmo_tdefs_reset(tdefs);
 	print_tdef_info(7);