galley proof vs test copy

galley proof and test copy both are nouns.

Word	Noun	Adjective	Verb	Adverb
galley proof	Yes	No	No	No
test copy	Yes	No	No	No

As nouns, test copy is a hypernym of galley proof; that is, test copy is a word with a broader meaning than galley proof:

Other hypernyms of galley proof include proof, trial impression.

galley proof (noun)	test copy (noun)
a proof taken before the type is broken up to print pages	(printing) an impression made to check for errors