return FilePredicate.IS_DIRECTORY;
  }

  /**
   * Returns a predicate that returns the result of {@link File#isFile} on input files.
   *
   * @since 15.0
   */
  public static Predicate<File> isFile() {
    return FilePredicate.IS_FILE;
  }

  private enum FilePredicate implements Predicate<File> {
    IS_DIRECTORY {
      @Override
      public boolean apply(File file) {

    File asciiFile = getTestFile("ascii.txt");
    File dir = asciiFile.getParentFile();
    assertTrue(Files.isDirectory().apply(dir));
    assertFalse(Files.isFile().apply(dir));

    assertFalse(Files.isDirectory().apply(asciiFile));
    assertTrue(Files.isFile().apply(asciiFile));
  }

  /** Returns a root path for the file system. */
  private static File root() {
    return File.listRoots()[0];
  }

    File asciiFile = getTestFile("ascii.txt");
    File dir = asciiFile.getParentFile();
    assertTrue(Files.isDirectory().apply(dir));
    assertFalse(Files.isFile().apply(dir));

    assertFalse(Files.isDirectory().apply(asciiFile));
    assertTrue(Files.isFile().apply(asciiFile));
  }

  /** Returns a root path for the file system. */
  private static File root() {
    return File.listRoots()[0];
  }