certify vs testify

certify and testify both are verbs.

Word	Noun	Adjective	Verb	Adverb
certify	No	No	Yes	No
testify	No	No	Yes	No

As verbs, testify is a hypernym of certify; that is, testify is a word with a broader meaning than certify:

certify: provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes
testify: provide evidence for

Other hypernyms of certify include bear witness, evidence, prove, show.

certify (verb)	testify (verb)
provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes	give testimony in a court of law
declare legally insane	provide evidence for
guarantee payment on; of checks
guarantee as meeting a certain standard
authorize officially