code: func (a Afero) TempDir(dir, prefix string) (name string, err error) {
  	return TempDir(a.Fs, dir, prefix)
  }
docs: // TempDir creates a new temporary directory in the directory dir
  // with a name beginning with prefix and returns the path of the
  // new directory.  If dir is the empty string, TempDir uses the
  // default directory for temporary files (see os.TempDir).
  // Multiple programs calling TempDir simultaneously
  // will not choose the same directory.  It is the caller's responsibility
  // to remove the directory when no longer needed.