good authority vs testimony

good authority and testimony both are nouns.

Word	Noun	Adjective	Verb	Adverb
good authority	Yes	No	No	No
testimony	Yes	No	No	No

As nouns, testimony is a hypernym of good authority; that is, testimony is a word with a broader meaning than good authority:

Other hypernyms of good authority include testimonial.

good authority (noun)	testimony (noun)
testimony by someone who should know	a solemn statement made under oath
	an assertion offering firsthand authentication of a fact
	something that serves as evidence