See this comment for background:
https://github.com/openshift/origin/blob/6b07170abad135bc7c5b22c78b2079ceecfc8b51/test/extended/etcd/vertical_scaling.go#L75-L86

The current vertical scaling test relies triggers CPMSO to create a new machine by first deleting an existing machine. In that test we can't validate that the new machine is scaled-up before the old one is removed.

Another test we could add is to first disable the CPMSO and then delete an existing machine and manually create a new machine like we did before the CPMSO.

https://docs.openshift.com/container-platform/4.16/machine_management/control_plane_machine_management/cpmso-disabling.html

That way we can validate that the scale-down does not happen before the scale-up event.