I think I have my comments in order by now:
- ActivityPub is easy to implement. Simply follow my tutorial and you are up and running. This does not implement all the parts you want. But it implements the ActivityPub part.
- ActivityPub is awful to test. The specification is full of holes, e.g. replies are not mentioned. So you will be doing a lot of specification work if you are testing it. For other things the specification is overly precise, e.g. when POST to outbox, the assigned id must be in the Location header. Finally, the real value of the specification is introducing Actors, which is on a third abstraction level from the two already mentioned.
- One could probably get a good test suite together by going over Diaspora*'s features. The main issue is to ensure that one makes them Diaspora independent. However, this would not be an ActivityPub Test Suite, but one for a general social media site.
- I am unsure how frequent testing is in various implementations. It might be much more useful to migrate certain tests to a common basis such as Gherkin than starting a new test suite.