What's the noun for testifiable? Here's the word you're looking for.
testament
(law) A solemn, authentic instrument in writing, by which a person declares his or her will as to disposal of his or her inheritance (estate and effects) after his or her death, benefiting specified heir(s).
“The number of visits to Susan's web site was a testimonial to how many caring friends she had and their interest in her well being.”
“Having come upon the work at this later date, Buchanan decided to publish it as a testimonial to his own affection for the King to whom he had been a tutor.”
“If you're asking for a testimonial to her character as a mother and as a hard-working local member, I'd be very happy to provide one.”
“The criticisms of his testimony and the points derived from the documentation are not, in my view, of sufficient force to cause me to reject that evidence.”
“Campaigners said all three breakthroughs were testimony to Scotland's position in the forefront of international cancer research.”
“The pictures of Gandhi, created with dots and stencil print, stand testimony to the artistic acumen of these students.”
“All questions of testacy or intestacy belong to the judge of the domicile.”
“Nevertheless, significant interarea differences in patterns of rights creation or in the distribution of property will not be reducible to differences in rates of testacy.”