We have a few things that we cache on a ReviewRequest in order to

speed up repeated lookups (particulary for the review request page),

with more coming. These caches are on the object itself, so there's no

shared state between separate representations of the same review

request, but it helps to avoid a lot of repeated database queries.
The problem is, when a draft is published or discarded we don't clear

all this state. We do clear the file attachment state, but not the

review request blocks list, approval states, or loaded diffsets. This

isn't a major issue outside of unit tests, but could pose confusing

problems in the future, and will be getting worse with upcoming changes.
We now have a new function designed to clear local caches on the object:

ReviewRequest.clear_local_caches(). This doesn't need to be called

manually, but is called whenever a review request is published or a

draft is otherwise deleted.
It's worth noting that the deletion of a draft only resets caches for

the ReviewRequest object directly associated with it in memory, and

not any other instances in memory. This is fine for the purposes of

these caches.
Several missing unit tests for functions on ReviewRequest have been

added to test the basic caching functionality and the cache reset.

All unit tests pass.