### Question:
ConvertUtils { public static void validateIsHexString(String input) { if (input == null) { throw new IllegalArgumentException("Null is not a valid hex"); } if (!isHexString(input)) { throw new IllegalArgumentException(input + " is not a valid hex"); } } private  ConvertUtils(); static byte[] getBytes(final String hexString); static String toHex(final byte[] bytes); static String padHex(final String hex, int hexStringSize); static byte[] fromHexToBytes(String hexString); static Pair<String, Integer> xorValues(String originalValue, String newValue); static String fromHexToString(final String hexString); static String fromStringToHex(final String plainText); static String toSize16Hex(final BigInteger number); static void validateNotNegative(final BigInteger number); static void validateNotNegative(final long number); static String toString(final BigInteger number); static BigInteger toUnsignedBigInteger(long value); static BigInteger toUnsignedBigInteger(BigInteger value); static boolean isHexString(String input); static void validateIsHexString(String input); static void validateIsHexString(String input, Integer size); static String reverseHexString(String hex); static byte[] xor(byte[] b1, byte[] b2);  }### Answer:
@Test void validateIsHexString() { assertIsHexString("026ee415fc15", null, null); assertIsHexString("abcdef0123456789ABCDEF", null, null); assertIsHexString("026ee415fc15", 12, null); assertIsHexString("abcdef0123456789ABCDEF", 22, null); assertIsHexString("026ee415fc15", 4, "026ee415fc15 is not an hex of size 4"); assertIsHexString( "abcdef0123456789ABCDEF", 4, "abcdef0123456789ABCDEF is not an hex of size 4"); assertIsHexString("abcdef012345G789ABCDEF", null, "abcdef012345G789ABCDEF is not a valid hex"); assertIsHexString("026ee415fc1", null, "026ee415fc1 is not a valid hex"); assertIsHexString(null, null, "Null is not a valid hex"); assertIsHexString("abcdef012345G789ABCDEF", 2, "abcdef012345G789ABCDEF is not a valid hex"); assertIsHexString("026ee415fc1", 2, "026ee415fc1 is not a valid hex"); assertIsHexString(null, 2, "Null is not a valid hex"); }