the caching is triggered by `li.blog.get`, but it is done in parallel without blocking the
command, thus there is a possibility that the data is not yet in cache when the following
test is done.
A loop with delay is done, to be sure that cache is filled before doing the assertion.
items are stored in chronological order in Pubsub, and as we want the more recent one, we
need to set `before=''`. Otherwise, we can get a wrong item from a previous test.
RSM `max` alone will return first (oldest) items, while `max_items` will return latest
ones. As Libervia Pubsub as been fixed in this regard, tests are now fixed too.
