main PR:
and two follow up PRs:

We decided to write a backend integration test to include reporting.

 my reasoning was that given the fact that the feature is self-contained in deployments, there is no point in writing a backend integration test. Anyway, I leave the decision to you.

 we can test in in the deployments acceptance tests or in the backend integration; not much difference to me, tbh

I'm not sure why it was 13SP (I know I was estimating it, but looks like I didn't pay enough attention to this epic);

5 SP should be enough to test it;
I think the test plan should be more or less like this:

• create deployment with at least two different artifacts;

• call deployments/next pretending we're using at least three devices which will get two different artifacts;

• check the list of devices contains info about selected artifacts;

• verify deployments info (statistics or main deployments object - whatever we'll decide to do during implementation) contains sum of artifacts size for all device deployments

 why integration test? I believe an acceptance test would be enough.