Developing a disaster recovery plan is a waste of time and resources if it is not tested regularly, thoroughly, and frequently (frequently depends on any changes in your organization's functions and environment). The goal of disaster recovery testing is not to pass a test but to find out what does not work. Design your tests to find problems because it is better to find them during a test than during an actual recovery situation.
Testing can be as simple as calling all of the phone numbers in an emergency notification list to verify that everyone can be reached when needed. Or testing can be as complex as actually conducting operations at a recovery site to ensure that everything works correctly. Between those extremes, variations include walkthroughs, during which everyone involved in the recovery process discusses their roles in a moderated recovery scenario, and simulations that initiate the recovery plan but use simulated data. Using a combination of testing scenarios to test specific parts of the plan also can be effective.