Simple check to confirm access to a Domain Controller

I'm preparing for a battery of resilience tests on a new network (which will be hosting a mission-critical application).

As part of it, I ought to confirm the resilience of the domain controllers. We have 2 DCs in this environment, and I need to be able to confirm that when I pull the plug on one, the remaining DC takes up the slack.

What is the simplest test I can do to confirm DC2 is successfully covering for DC1?

Would something as simple as gpupdate /force suffice? Or is there a better, simple test? We've got a lot to test so the less we need to do, the better.

You can run the following commands:

Query the domain for the current Primary Domain Controller

NETDOM QUERY /D:%USERDNSDOMAIN% PDC

Query the domain for the current list of FSMO owners

NETDOM QUERY /D:%USERDNSDOMAIN% FSMO

The commands will return the active PDC and DC(s) responsible for various FSMO roles.