IdUtil { public static BigInteger fromString(final String idString) { if (Strings.isNullOrEmpty(idString)) { return null; } return new BigInteger(idString, 16); } private  IdUtil(); static BigInteger fromString(final String idString); static String toString(final BigInteger id); static BigInteger next();  }
@Test(expected = IllegalArgumentException.class) public void testMalformedIdFromString() { IdUtil.fromString("notBase16String"); }