How to send A and B messages at the same time?
What I did was to keep big batches (bigger than the test groups) and allow to run several jobs, and then:

drupal_root=/var/www/drupal

*/5 * * * * www-data nice -n19 /usr/bin/drush -u 1 -r $drupal_root civicrm-api job.process_mailing auth=0 -y -l wemove
*/5 * * * * www-data nice -n19 /usr/bin/drush -u 1 -r $drupal_root civicrm-api job.process_mailing auth=0 -y -l wemove