In conjunction with A/B website testing, the importance of agility in the testing approach became even more important. Where speed matters and code base is changing every minute, there is no time for over planning nor bug hunting without clear focus.
A/B testing aims for conversion optimization, the Agile Tester plays where conversion happens. High traffic pages in the conversion funnel always will always be on top of his investigation list. Reliability of crucial features come right after that. Website localization in combination with A/B testing are common on larger websites and a challenge for the Agile Tester, not only technically but as well in prioritization matters. Not every clever localized feature might attract the highest traffic and some languages and IP countries will simply not be able to concur with the top 5 in terms of visitors.
As A/B testing comes typically with rich realtime data which is in the optimal case broken down to meaningful groups it is as well a great treasure trove for Agile Testers. Many hints for broken functionality can be found here and guide his investigation focus.
Functional and explorative testing are his preferred playgrounds although he acknowledges the need of well thought automation where it safes time and effort. Finding the right balance between automation and manual testing is crucial for every QA/testing team. Doing it right means to be able to adjust flexibly and to leave overcome believes or processes behind whenever needed and beneficial.