Wipe out the entire database. Verify that a backup can be installed and used properly. Do you also have logs that record transactions? Can you find out why the DB was wiped out and which user profile did it? Will you need to?
Drop a connection between your server and the mainframe (or between the server and database.) Verify that when you attempt to restablish the connection, everything works properly (jobs restarted, nothing hanging.)
Crash the server (or just unplug it) during a transaction. Reboot and verify that nothing got severly jacked up.
If it can rollover to a redundant server then you want cause the conditions that warrant a rollover, make sure the rollover occurs and verify that the correct data is on the rollover server (that depends on how often the data is replicated.)