Use physical standby for testing

Assuming a guaranteed restore point was used, after the Standby has been Primary for a while, this will return it to being a Standby

 shutdown abort;
 startup mount;
 select name from v$restore_point;
 flashback database to restore point DRTEST;
 alter database convert to physical standby;
 shutdown abort;
 startup nomount;
 alter database mount standby database;
 alter database recover managed standby database disconnect;