You can A/B test the Facebook copy and title at the same time by following these steps:
1. Go to Campaign 'Editor' tab
2. Paste this code into the Facebook share message field:
{% assign facebook_title_and_copy = "facebook_title_and_copy" | ab_test: "A", "B" %}
{% if facebook_title_and_copy == "a" %}
Input share message copy for A here.
{% else %}
Input share message copy for B here.
{% endif %}
3. Go to Facebook share title and add this into the input:
{% assign facebook_title_and_copy = "facebook_title_and_copy" | ab_test: "A", "B" %}
{% if facebook_title_and_copy == "A" %}
Input title copy for A here.
{% else %}
Input title copy for B here.
{% endif %}
4. Save changes.