I'm not sure it's needed either. An older, Taiwanese teak decked trawler is going to leak - you don't need a test to determine that
. If not leaking through to the interior (best case), leaking into the deck material (worst case).
A more sure test used in the RV biz is the 'blower test' in which a blower or vacuum cleaner is attached after all the known openings are sealed with tape. On a typical trawler, it may not work cause there will be so many leaks you won't be able to hold any pressure.