### Question:
ConstantUtil { static Set<? extends Class<? extends NativeEnum>> getNativeEnumClassesManually() { return NATIVE_ENUM_CLASSES; } private  ConstantUtil();   }### Answer:
@Test void getNativeEnumClassesManuallyIsImmutable() { final Set<? extends Class<? extends NativeEnum>> nativeEnumClassesManually = ConstantUtil.getNativeEnumClassesManually(); Assertions.assertThrows(UnsupportedOperationException.class, () -> nativeEnumClassesManually.add(null)); Assertions.assertThrows(UnsupportedOperationException.class, () -> nativeEnumClassesManually.removeIf(o -> true)); }
@Test void getNativeEnumClassesManuallyIsSameInstance() { final Set<? extends Class<? extends NativeEnum>> nativeEnumClassesManually = ConstantUtil.getNativeEnumClassesManually(); final Set<? extends Class<? extends NativeEnum>> nativeEnumClassesManually2 = ConstantUtil.getNativeEnumClassesManually(); Assertions.assertSame(nativeEnumClassesManually, nativeEnumClassesManually2); }