protected static String getReverseZoneNetworkAddress(String baseIp, int range,
      int index) throws UnknownHostException {
    if (index < 0) {
      throw new IllegalArgumentException(
          String.format("Invalid index provided, must be positive: %d", index));
    }
    if (range < 0) {
      throw new IllegalArgumentException(
          String.format("Invalid range provided, cannot be negative: %d",
              range));
    }
    return calculateIp(baseIp, range, index);
  }
@Test
  public void testThrowUnknownHostExceptionIfIpIsInvalid() throws Exception {
    exception.expect(UnknownHostException.class);
    ReverseZoneUtils
        .getReverseZoneNetworkAddress("213124.21231.14123.13", RANGE, INDEX);
  }