I always encourage testing because it's possible to have fatal anesthesia reactions even if a person has never shown symptoms. In fact at least one study mentioned that carriers of recessive mutations may also be susceptible to anesthesia reactions.
Once you know which mutation (Thomsen's) or mutations (Becker's) you have, then other family members can be tested just for those mutations and it is much cheaper. Fullerton Genetics in North Carolina is a good lab for testing specific mutations.