Regularly practicing disaster recovery procedures to ensure they work when needed. Like fire drills that prepare you for real emergencies.
Companies perform quarterly DR tests where they intentionally switch to backup systems to verify recovery plans work correctly.
DR Testing is a process/practice, not a single cloud service. All major clouds support DR testing using their backup, replication, DNS/failover, and automation services (e.g., AWS Elastic Disaster Recovery, Azure Site Recovery, Google Cloud Backup and DR, OCI Full Stack Disaster Recovery), but the term refers to the regular exercise of your recovery plan regardless of provider.