I wouldn't take "deriving" as being as "strong" a process as "proving", but that's just my gut; I don't have authoritative definitions to back me up. Proofs have rules and requirements. Derivations are, I think, more a matter of figuring or simplifing from a given point. A derivation would likely often be useful in figuring out how to prove something, though.
It might help if you clarified what you're talking about. You say you "made" a test. Do you mean that you're the instructor, and your collegues are questioning your instrument's design and/or wording, suggesting that you revise it before administering it to your students? You refer to "proving the deriviative[sic] of sin[sic] and tan[sic]". What does this mean? Are you finding "derivatives", or deriving some identity, or what?
Thank you.
Eliz.