def handle_get_vts_command(self, vt_et):
        """ Handles <get_vts> command.

        @return: Response string for <get_vts> command.
        """

        vt_id = vt_et.attrib.get('vt_id')
        vt_filter = vt_et.attrib.get('filter')

        if vt_id and vt_id not in self.vts:
            text = "Failed to find vulnerability test '{0}'".format(vt_id)
            return simple_response_str('get_vts', 404, text)

        filtered_vts = None
        if vt_filter:
            filtered_vts = self.vts_filter.get_filtered_vts_list(
                self.vts, vt_filter)

        responses = []

        vts_xml = self.get_vts_xml(vt_id, filtered_vts)

        responses.append(vts_xml)

        return simple_response_str('get_vts', 200, 'OK', responses)
Handles <get_vts> command.

        @return: Response string for <get_vts> command.