Aggregate reporting for A/B testings helps you understand the totals of opens, clicks, or conversions across all the A/B variants in one view. Each test send, test variant, and winning email generates its own Single Mailing Report.
Additionally, from your A/B Test status page, you can view some of the completed and ongoing email metrics such as unique open %, unique click %, unique conversion % , and effective rate of each of your test variants. Completed metrics show what the email metrics were when the winner was determined. Whereas ongoing metrics reflect the current counts of those metrics.