attest vs testify

attest and testify both are verbs.

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

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

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

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

As verbs, attest and testify are synonyms defined as:

Other synonyms of attest include bear witness, take the stand.

attest (verb)	testify (verb)
authenticate, affirm to be true, genuine, or correct, as in an official capacity	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
give testimony in a court of law
establish or verify the usage of