func (b *storeManagerTestBacking) updateEntity(info multiwatcher.EntityInfo) {
	b.mu.Lock()
	defer b.mu.Unlock()
	id := info.EntityId()
	b.entities[id] = info
	b.txnRevno++
	if b.watchc != nil {
		b.watchc <- watcher.Change{
			C:     id.Kind,
			Id:    ensureModelUUID(id.ModelUUID, id.Id),
			Revno: b.txnRevno, // This is actually ignored, but fill it in anyway.
		}
	}
}

// Update updates the information for the given entity.
func (a *multiwatcherStore) Update(info multiwatcher.EntityInfo) {
	id := info.EntityId()
	elem := a.entities[id]
	if elem == nil {
		a.add(id, info)
		return
	}
	entry := elem.Value.(*entityEntry)
	// Nothing has changed, so change nothing.
	// TODO(rog) do the comparison more efficiently.
	if reflect.DeepEqual(info, entry.info) {
		return
	}
	// We already know about the entity; update its doc.
	a.latestRevno++
	entry.revno = a.latestRevno
	entry.info = info
	a.list.MoveToFront(elem)
}