### Question:
I18n { public static Set<Locale> getLocalizationProblemLocales( Class<?> i18nClass ) { CheckArg.isNotNull(i18nClass, "i18nClass"); Set<Locale> locales = new HashSet<Locale>(LOCALE_TO_CLASS_TO_PROBLEMS_MAP.size()); for (Entry<Locale, Map<Class<?>, Set<String>>> localeEntry : LOCALE_TO_CLASS_TO_PROBLEMS_MAP.entrySet()) { for (Entry<Class<?>, Set<String>> classEntry : localeEntry.getValue().entrySet()) { if (!classEntry.getValue().isEmpty()) { locales.add(localeEntry.getKey()); break; } } } return locales; } private  I18n( String id,
                  Class<?> i18nClass ); static Set<Locale> getLocalizationProblemLocales( Class<?> i18nClass ); static Set<String> getLocalizationProblems( Class<?> i18nClass ); static Set<String> getLocalizationProblems( Class<?> i18nClass,
                                                       Locale locale ); static LocalizationRepository getLocalizationRepository(); static void setLocalizationRepository( LocalizationRepository localizationRepository ); static void initialize( Class<?> i18nClass ); String id(); boolean hasProblem(); boolean hasProblem( Locale locale ); String problem(); String problem( Locale locale ); String text( Object... arguments ); String text( Locale locale,
                        Object... arguments ); @Override String toString();  }### Answer:
@Test( expected = IllegalArgumentException.class ) public void shouldFailToGetLocalizationProblemLocalesIfNoClassSupplied() { I18n.getLocalizationProblemLocales(null); }
@Test public void shouldNeverReturnNullWhenGettingLocalizationProblemLocales() { assertThat(I18n.getLocalizationProblemLocales(TestI18n.class), notNullValue()); }