Where can I find the A/B Testing feature?

The A/B Test feature is a part of the newsletter creation process. Whenever you
create a newsletter message, you will find it at the bottom of the first page.
Turn on the A/B Test switch button to enable it. Once enabled, the newsletter
creator will be extended with additional steps where you define the type of test
and its settings.

If you wish to disable the A/B Test simply go back to the message settings and
switch the test to OFF.