See testify in Webster's New World Roget's A-Z Thesaurus II
To give evidence or testimony under oath:
attest, swear, witness. (Law) depone, depose. Idioms: bear witness, take the stand. See lawTo confirm formally as true, accurate, or genuine:
attest, certify, vouch (for), witness. Idiom: bear witness to. See affirmTo assure the certainty or validity of.
Also used with to: attest, authenticate, back (up), bear out, confirm, corroborate, evidence, justify, substantiate, validate, verify, warrant. See support, trueTo give grounds for believing in the existence or presence of:
argue, attest, bespeak, betoken, indicate, mark, point to, witness. See showLearn more about testify