@Test
    void rfc_5869_test_vector_case_2() {
        var ikm  = unhex("000102030405060708090a0b0c0d0e0f" +
                         "101112131415161718191a1b1c1d1e1f" +
                         "202122232425262728292a2b2c2d2e2f" +
                         "303132333435363738393a3b3c3d3e3f" +
                         "404142434445464748494a4b4c4d4e4f");
        var salt = unhex("606162636465666768696a6b6c6d6e6f" +
                         "707172737475767778797a7b7c7d7e7f" +
                         "808182838485868788898a8b8c8d8e8f" +
                         "909192939495969798999a9b9c9d9e9f" +
                         "a0a1a2a3a4a5a6a7a8a9aaabacadaeaf");
        var info = unhex("b0b1b2b3b4b5b6b7b8b9babbbcbdbebf" +
                         "c0c1c2c3c4c5c6c7c8c9cacbcccdcecf" +
                         "d0d1d2d3d4d5d6d7d8d9dadbdcdddedf" +
                         "e0e1e2e3e4e5e6e7e8e9eaebecedeeef" +
                         "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff");

        var hkdf = HKDF.extractedFrom(salt, ikm);
        var okm = hkdf.expand(82, info);
        assertEquals("b11e398dc80327a1c8e7f78c596a4934" +
                     "4f012eda2d4efad8a050cc4c19afa97c" +
                     "59045a99cac7827271cb41c65e590e09" +
                     "da3275600c2f09b8367793a9aca3db71" +
                     "cc30c58179ec3e87c14c01d5c1f3434f" +
                     "1d87",
                     hex(okm));
    }
HKDF tests that ensure that the output of our own implementation matches the test
vectors given in <a href="https://tools.ietf.org/html/rfc5869">RFC-5869</a>.

We don't expose the internal PRK (pseudo-random key) value of the HKDF itself,
so we don't test it explicitly. The actual OKM (output keying material) inherently
depends on it, so its correctness is verified transitively.

@author vekterli
security-utils/src/test/java/com/yahoo/security/HKDFTest.java