WordNet sense 1 ((printing) an impression made to check for errors):

test copy, trial impression

WordNet sense 2 (any factual evidence that helps to establish the truth of something):

cogent evidence

WordNet sense 3 (not admitting of passage or capable of being affected):

impervious, imperviable

WordNet sense 4 (read for errors):

proofread

WordNet sense 5 (the act of validating; finding or testing the truth of something):

substantiation, validation