@Override
  public KeyData newKeyData(ByteString serializedKeyFormat) throws GeneralSecurityException {
    throw new UnsupportedOperationException("not needed for tests");
  }
@param serializedKey serialized {@code HmacPrfKey} proto
java_src/src/main/java/com/google/crypto/tink/prf/internal/LegacyHmacPrfTestKeyManager.java