Test it

The best way to test the failover aka High Availability option is to find out on which node your VM is running and then turn it off.

My Windows 7 is on HC1

Turn off HC1.

And after a little bit of waiting... He's on HC2.

And then there's the lesson of always having a backup ready, because even failover didn't save this machine ;) In all fairness, it was mid installation!