comments: Test author updates logic.

[amass01]

#1491 added new complexity to the pi plugin to support author updates.

In order to achieve that pi plugin uses external calls to other plugins, currently
we don't have a framework in place to test such scenarios.

This issue is a reminder to remind us to cover this logic when we have the test framework
which allows external plugin calls in place.

[lukebp]

Blocked by #1494.