Hi,
Acymailing v9 is built around the new drag & drop editor. The html editor is just there as a courtesy so you can still edit your templates and campaigns that are migrated from v5. So if you want to use the A/B testing you must use the drag & drop editor, it doesn't work with html templates.
Since the future of Acymailing is at the drag & drop editor A/B testing for html templates is not to be expected.
i suggest you recreate your templates and campaigns in the drag & drop editor so you can take full advantage of the Acymailing features.