There are several ways that Pencil can support with A/B testing:
Pencil is able to help you rapidly generate image generations and text generations which allows you to produce a large number of variations for A/B testing in a short space of time.
If you have your ad accounts connected you can manually tag ads into test groups and compare those test groups across a huge number of data points drawn from your ad channels.
Pencil compares performance across the test groups you define. It does not allocate audiences or run controlled split tests.