Different ways to do this & it's been a while since I've done this, previous example using unload and load works well.
To do this in a single step, I think you must specify the DB name@instance name

wner of the DB in single quotes.table name of the table you're selecting data from.
This assumes the target table in the test DB already exists and whatever SQL tool you're using is accessing the testDB.
Example: insert into ren_option_invite
select * from live@prod-instance:'sysadm'.ren_option_invite