Which are better ways to test the BCP?

Answer: Theoretically, the best way to test your business continuity plan would be the so-called "Full-scale exercise" - it simulates the real incident as closely as possible, and includes not only your organization but also your partners and suppliers who have some role in business continuity.

Of course, it would be very difficult to organize such a test in large organization, at least in the beginning - therefore, the best would be to start with easier tests (checklists, tabletop exercises), and gradually throughout the years progress towards more complex way of test ing.

You can find additional information about testing and exercising in A.8 of NFPA 1600-2013 Annex A, or in PD 25666:2010 (Guidance on exercising and testing for continuity and contingency programmes).