### Question:
FileSystemUtil { public static void registerFileSystems(@Nonnull final Iterable<FileSystem> fileSystems, @Nonnull final Configuration conf) { for (final FileSystem fs : fileSystems) { try { final String scheme = fs.getScheme(); final Class clazz = fs.getClass(); log.debug("Found {} FileSystem using class: {}", scheme, clazz); conf.setClass("fs." + scheme + ".impl", clazz, FileSystem.class); } catch (final Exception e) { log.warn("Cannot load FileSystem using class: {}: {}", fs.getClass().getName(), e, e); } } } private  FileSystemUtil(); static boolean fileExists(@Nonnull final URI uri, @Nonnull final Configuration conf); @Nonnull static URL parseUrl(@Nonnull final String s, @Nullable final Configuration conf); static void registerFileSystems(@Nonnull final Iterable<FileSystem> fileSystems, @Nonnull final Configuration conf);  }### Answer:
@Test public void registerFileSystems() { final Configuration conf = new Configuration(false); FileSystemUtil.registerFileSystems(Arrays.asList(new LocalFileSystem(), new MockFileSystem(), new RawLocalFileSystem()), conf); Assert.assertEquals(LocalFileSystem.class.getName(), conf.get("fs.file.impl")); Assert.assertEquals(MockFileSystem.class.getName(), conf.get("fs.mock.impl")); }