testify vs certify

testify and certify both are verbs.

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

As verbs, certify is a hyponym of testify; that is, certify is a word with a more specific, narrower meaning than testify:

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

Other hyponyms of testify include attest, demonstrate, evidence, manifest, presume, abduce, adduce, cite.

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