Hi @InfraSolutions ,
to successfully test every feature of an Azure Load Balancer in my opinion you need at least 2 backend instances (could be the smallest VM SKU that your backend role requires). This way it's possible to test the "automated failover" if one backend device is going down and also this offers to verify the the workload is properly balanced between both backend devices.
If you don't need the backend VMs it's possible to stop the VMs to reduce costs. You will be charged for the disk resources only, if the Azure VMs are all deallocated. For testing based on the required tests you can start one or both VMs.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten