It was recently confirmed to me by support that Champion/Challenger tests can only be used with trigger campaigns. While I understand that there are other A/B test capabilities, Champion/Challenger tests are very easy to set up and execute, and lead to more efficient testing across the board.
The fact that they can only be used with trigger campaigns unearthed another limitation for those of us using programs in engagement programs... You cannot do Champion/Challenger tests here either, because they are batch campaigns.
There was recently a bug that was allowing these tests in batch campaigns, so hopefully it wouldn't be too hard to implement this, and it would make testing much easier all-around!!