### Question:
LocaleHelper { @Nullable public static String getValidCountryCode (@Nullable final String sCode) { if (StringHelper.hasText (sCode)) { if (RegExHelper.stringMatchesPattern ("[a-zA-Z]{2}|[0-9]{3}", sCode)) { return sCode.toUpperCase (CGlobal.LOCALE_FIXED_NUMBER_FORMAT); } if (RegExHelper.stringMatchesPattern ("[a-zA-Z]{3}", sCode)) { final String sAlpha3 = sCode.toUpperCase (CGlobal.LOCALE_FIXED_NUMBER_FORMAT); final String sAlpha2 = COUNTRY_ISO3TO2.get (sAlpha3); return sAlpha2 != null ? sAlpha2 : sAlpha3; } } return null; } private  LocaleHelper(); @Nonnull static String getLocaleDisplayName(@Nullable final Locale aLocale, @Nonnull final Locale aContentLocale); @Nonnull static String getLocaleNativeDisplayName(@Nonnull final Locale aLocale); @Nonnull @ReturnsMutableCopy static ICommonsMap <Locale, String> getAllLocaleDisplayNames(@Nonnull final Locale aContentLocale); @Nonnull @ReturnsImmutableObject @CodingStyleguideUnaware static List <Locale> getCalculatedLocaleListForResolving(@Nonnull final Locale aLocale); @Nonnull static Locale getLocaleFromString(@Nullable final String sLocaleAsString); @Nullable static Locale getLocaleToUseOrNull(@Nonnull final Locale aRequestLocale, @Nonnull final Collection <Locale> aAvailableLocales); @Nullable static Locale getLocaleToUseOrFallback(@Nonnull final Locale aRequestLocale,
                                                 @Nonnull final Collection <Locale> aAvailableLocales,
                                                 @Nullable final Locale aFallback); static boolean isSpecialLocale(@Nullable final Locale aLocale); static boolean isSpecialLocaleCode(@Nullable final String sLocale); @Nullable static String getValidLanguageCode(@Nullable final String sCode); @Nullable static String getValidCountryCode(@Nullable final String sCode); @Nonnull static EChange clearCache(); static final char LOCALE_SEPARATOR; static final String STR_ALL; static final Locale LOCALE_ALL; static final String STR_INDEPENDENT; static final Locale LOCALE_INDEPENDENT; }### Answer:
@Test public void testGetValidCountryCode () { assertNull (LocaleHelper.getValidCountryCode (null)); assertNull (LocaleHelper.getValidCountryCode ("")); assertNull (LocaleHelper.getValidCountryCode ("1")); assertNull (LocaleHelper.getValidCountryCode ("12")); assertNull (LocaleHelper.getValidCountryCode ("a")); assertNull (LocaleHelper.getValidCountryCode (" ")); assertNull (LocaleHelper.getValidCountryCode ("_")); assertNull (LocaleHelper.getValidCountryCode ("_de")); assertNull (LocaleHelper.getValidCountryCode ("d.e")); assertNull (LocaleHelper.getValidCountryCode ("d e")); assertNotNull (LocaleHelper.getValidCountryCode ("abc")); assertNull (LocaleHelper.getValidCountryCode ("abcd")); assertNull (LocaleHelper.getValidCountryCode ("1234")); assertEquals ("DE", LocaleHelper.getValidCountryCode ("De")); assertEquals ("123", LocaleHelper.getValidCountryCode ("123")); assertEquals ("EN", LocaleHelper.getValidCountryCode ("en")); }