When starting to back-paginate, in this test, we:
- either have a previous-batch token, that points to the first event
*before* the message was sent,
- or have no previous-batch token, because we stopped sync before
receiving the first sync result.
Because of the behavior introduced in 944a9220, we don't restart
back-paginating from the end, if we've reached the start. Now, if we are
in the case described by the first bullet item, then we may backpaginate
until the start of the room, and stop then, because we've back-paginated
all events. And so we'll never see the message sent by Alice after we
stopped sync'ing.
One solution to get to the desired state is to clear the internal state
of the room event cache, thus deleting the previous-batch token, thus
causing the situation described in the second bullet item. This achieves
what we want, that is, back-paginating from the end of the timeline.
Benjamin Bouvier
fe9354a886