### Question:
HelperUtils { public static String[] splitMailAddress(String mailAddress) { mailAddress = StringUtils.defaultString(mailAddress).trim(); if (mailAddress.length() > 0) { return mailAddress.split("@"); } return null; } private  HelperUtils(); static Long parseTimeString(String input); static String parseStringTs(long ts_Active); static String addZero(int no); static boolean hasCorrectFormat(String input); static void parseEntryValue(Context context, Integer defaultNo); static List<String[]> getLanguageList(String[] availableLanguages, Context context, Result result,
                                                 Messages msg); static boolean checkEmailAddressValidness(String[] mailAddressParts, String[] domainList); static String[] splitMailAddress(String mailAddress); static String getHeaderText(final MimeMessage message); static byte[] readLimitedAmount(InputStream data, int maxSize);  }### Answer:
@Test public void testSplitMailAddress() { assertNull(HelperUtils.splitMailAddress(null)); assertNull(HelperUtils.splitMailAddress("")); assertNull(HelperUtils.splitMailAddress(" ")); String[] parts = HelperUtils.splitMailAddress("foo"); assertNotNull(parts); assertEquals(1, parts.length); parts = HelperUtils.splitMailAddress("foo@bar"); assertNotNull(parts); assertEquals(2, parts.length); }