- This will not bring down your production environment and recommended to perform in an isolated network to avoid conflicts.
- This will keep the replication going to cloud from your source (in your scenario On-Premise).
- If you make any changes in your test environment such as un-installing AD/Removing a user account - This will not impact (No reverse sync from cloud to On-prem) the source infra.
- Please remember you can make changes inside these test environment, but do not delete test cloud infra such as complete VM/disk/VNet - This will create issues while you execute cleanup.
- You can perform test failover and clean up as many times as you need.
- Important : I understand that Domain Controller test failover is just an example that you picked, but it is not recommended to perform a direct failover for a DC in multi forest/domain environment, there are few considerations that you need to follow - more details here