Introduce tests to document current behavior of Pingback

Hi Julio, I'm sending this PR to you because Sergio is out of office during this week. 

This pull request is part of a serie of commits from @arboliveira with the objective to decouple the MB usages. A previous commit related to this one is already in master and it was committed under https://issues.liferay.com/browse/LPS-44579.

Let us know if you have any question.

Thanks