testimonial has 4 distinct synonyms spread across 3 of its 5 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
something that serves as evidence
“his effort was testimony to his devotion”
something that recommends (or expresses commendation of) a person or thing as worthy or desirable
2 of the 5 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for testimonial.
Synonyms, antonyms and the broader and narrower relations for testimonial come from Princeton University’s WordNet. Full sources and licences.