There are dozens of guides and tips on configuring ASA failover. Google it and you get several pages of results.
One good one (link) from our friend and contributor Pete Long suggest you set it up (he provides detailed instructions) and then just power off the active unit while traffic is actively passing through the firewall. That's a pretty dramatic test that proves the validity of the feature.
Active-Active is the licensed capability but using that requires your ASAs be in multiple context mode. Each context is Active-Standby with the roles reversed per context so the net effect is "Active-Active" for the overall firewall pair (but not for a given context).
So that's a bit of marketing doublespeak in most engineers' estimation.
