@Test
  public void testPoly1305TestVector9() throws GeneralSecurityException {
    byte[] key =
        Hex.decode("" + "02000000000000000000000000000000" + "00000000000000000000000000000000");
    byte[] in = Hex.decode("" + "fdffffffffffffffffffffffffffffff");
    Truth.assertThat(Poly1305.computeMac(key, in))
        .isEqualTo(Hex.decode("" + "faffffffffffffffffffffffffffffff"));
  }
Tests against the test vector 9 in Appendix A.3 of RFC 7539.
https://tools.ietf.org/html/rfc7539#appendix-A.3
java_src/src/test/java/com/google/crypto/tink/aead/internal/Poly1305Test.java