We have everything we need in test server to do the cloning ie. all the RMAN Backup pieces. Then why does RMAN connect to the source DB ?
rman target sys/passwd@SID_OF_SOURCE_DB auxiliary /
Backup-based duplication without a target connection RMAN creates duplicate files from pre-existing RMAN backups and copies. The DUPLICATE command must have been issued with the DATABASE clause. This form requires a connection to an auxiliary instance and a recovery catalog. This mode is useful when the target database is not available or a connection to it is not desirable (as mandated by security policy restrictions or a firewall).
Backup-based duplication without connection to target and recovery catalog RMAN creates duplicate files from RMAN backups and copies that were placed in a designated BACKUP LOCATION.