### Question:
VFSRegistryHelper { public String md5Hex(String content) { if (content == null) { return ""; } return DigestUtils.md5Hex(content); } VFSRegistryHelper(); @Inject  VFSRegistryHelper(final VFSMarshallerRegistry marshallerRegistry,
                             final @Named("ioStrategy") IOService ioService,
                             final @Named("systemFS") FileSystem fileSystem); Path ensureDirectory(final String directory); String md5Hex(String content); void storeEntry(final Path path,
                           final Object value); Object readEntry(final Path path); List<Object> readEntries(final Path rootPath,
                                    final DirectoryStream.Filter<Path> filter); void writeBatch(final Path path,
                           final String content); void deleteBatch(final Path path);  }### Answer:
@Test public void testMd5Hex() { String result = registryHelper.md5Hex(null); assertEquals("", result); result = registryHelper.md5Hex(DIRECTORY_NAME); assertEquals(DigestUtils.md5Hex(DIRECTORY_NAME), result); }