Add specs for OpenSSL::KDF.pbkdf2_hmac

[herwinw]

A lot of error messages depend on the used OpenSSL version, so I had to be a bit lenient with the error matching.

[eregon]

Looks like there is one failure: https://github.com/ruby/spec/actions/runs/6472919326/job/17574520140?pr=1092

[andrykonchin]

suggestion: as far as salt/iterations/length... are passed as keyword arguments - using local variables seems excessive to me. It doesn't improve readability of a test and don't add context (as far as meaning is already expressed with keyword argument names) but makes test case longer:

    pass = "secret"
    key = OpenSSL::KDF.pbkdf2_hmac(pass, salt: "\x00".b * 16, iterations: 20_000, length: 16, hash: "sha1")
    
    key.should == "!\x99+\xF0^\xD0\x8BM\x158\xC4\xAC\x9C\xF1\xF0\xE0".b

[herwinw]

Yeah, I wasn't exactly proud of this repetitive code either.

Since it's mostly just a bunch of default with one argument changed or removed, I was thinking maybe it's better to create a set of defaults, and the tests should explicitly alter these values. Something like this:

before :each do
  @pass = "secret"
  @defaults = { salt: "\x00".b * 16, iterations: 20_000, ... }
end

it "works with 10_000 iterations do"
  key = OpenSSL::KDF.pbkdf2_hmac(@pass, **@defaults, iterations: 10_000)
  key.should == SOME_VALUE
end

This reduces the length of the tests, removes a lot of duplication, and makes it a bit more clear which parameter we're testing.

[herwinw]

I pushed an update with the defaults hash, I would think this is much clearer and concise.

[herwinw]

Today I Learned: the value of OpenSSL::VERSION is the version of the gem, and not the version of OpenSSL. The Windows issues have been fixed now.

[andrykonchin]

Could you please squash commits?

[herwinw]

Could you please squash commits?

They're squashed into a single commit.

[andrykonchin]

Thank you!

[eregon]

@herwinw FYI: 92f6df8