Fixed a failing test introduced in 918a16bc.

    def __len__(self):

        return self.size

    def _get_size(self):

        if not hasattr(self, '_size'):

    def _get_size_from_underlying_file(self):

        if hasattr(self.file, 'size'):

                self._size = self.file.size

            elif hasattr(self.file, 'name') and self.file.name is not None and os.path.exists(self.file.name):

                self._size = os.path.getsize(self.file.name)

            elif hasattr(self.file, 'tell') and hasattr(self.file, 'seek'):

            return self.file.size

        if hasattr(self.file, 'name'):

            try:

                return os.path.getsize(self.file.name)

            except (OSError, TypeError):

                pass

        if hasattr(self.file, 'tell') and hasattr(self.file, 'seek'):

            pos = self.file.tell()

            self.file.seek(0, os.SEEK_END)

                self._size = self.file.tell()

            size = self.file.tell()

            self.file.seek(pos)

            else:

            return size

        raise AttributeError("Unable to determine the file's size.")

    def _get_size(self):

        if hasattr(self, '_size'):

            return self._size

        self._size = self._get_size_from_underlying_file()

        return self._size

    def _set_size(self, size):