The Collaborative International Dictionary of English v.0.48:

Testable \Test"a*ble\, a. [See Testament.]
   1. Capable of being tested or proved.
      [1913 Webster]

   2. Capable of being devised, or given by will.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "testable":
   absolute, actual, admitting no question, confirmable, demonstrable,
   demonstratable, factual, historical, inappealable, incontestable,
   incontrovertible, indisputable, indubitable, irrefragable,
   irrefutable, provable, real, self-evident, unanswerable,
   unconfutable, undeniable, unimpeachable, unquestionable,
   unrefutable, verifiable