Write smart tests for hash functions

[omershlo]

unit test for hash functions should use test vectors and compare results. Right not we are just doing sanity checking.

[amanusk]

Extending these tests https://github.com/KZen-networks/curv/blob/ab4aed0e13425e8d6ba19819227b60e8085fb701/src/cryptographic_primitives/hashing/hash_sha256.rs#L40

https://github.com/KZen-networks/curv/blob/ab4aed0e13425e8d6ba19819227b60e8085fb701/src/cryptographic_primitives/hashing/hash_sha512.rs#L40

?

[omershlo]

yes