### Question:
Validator { public static void validateMessageId(String messageId) { notNull(messageId, "messageId cannot be null"); if (messageId.length() == 0) { throw new IllegalArgumentException("messageId cannot be empty."); } } private  Validator(); static void validateMessage(Object message); static void validateMessageId(String messageId); static void validateRetryCount(int retryCount); static void validateDelay(long delayInMilliSecs); static void validateQueue(String queue); static void validatePriority(String priority);  }### Answer:
@Test public void validateMessageId() { assertThrows(IllegalArgumentException.class, () -> Validator.validateMessageId(null)); }