For the actual migration, there are two steps: a test migration and a migration. To make sure everything's working as expected without impacting the on-premises machines, it is recommended to do a test migration. During a test migration, the on-premises machines remain operational and can continue replicating. You can also use the replicated test Azure VM to validate the migration process, perform app testing, and address any issues before full migration. It is recommended to do this at least once for every machine before it gets migrated.