In order to test whether the standby db will work fine in case of failure, we are going to failover to our standby db.As swicthover_status replied with swicthover not allowed to primary, i have decided the below steps:
1. Shutdown the primary DB.
2. Activate the standby as primary
3.Perform dml operation on new primary, when task will be done, the new primary will not longer be needed.
Now my task is, if i make a cold backup of standby db before making it primary, can i replace the cold backup after the task so that it behaves as standby db as it was before??? In this case i don't need to recreate the standby db.
Not likely. You would have several issues. This method is likely to make things worse instead of better. If you want to test failover make sure you have flashback working on both the Primary and the Standby sides.
After a failover you want to recover the Primary, the old Primary as a new Standby. Once that is working you get the two servers in SYNC and perform a switchover and the Primary and Standby are back the way they should be.
What you might consider is the cold backup method is a bogus test. This is not how it will go down in the real world. I believe the test should align as closely to what might occur in production as possible.
Failover is also something you should give a lot of thought to. I have databases where if the outage is around 5 minutes or less the failover is more trouble and more risk than its worth. I have others where they need to be up 24/7. Ask yourself if you can do a switchover instead. What are your other options? Its great to have a failover plan and be ready, but the less you use it the better I say.