ItemRecommender recommender = rec.getItemRecommender();
assert recommender != null;
List<ScoredId> recs = recommender.recommend(1, -1);
assertTrue(recs.isEmpty());
recs = recommender.recommend(2, 2);
assertThat(Lists.transform(recs, ScoredIds.idFunction()),
containsInAnyOrder(9L));
recs = recommender.recommend(2, -1);
assertThat(Lists.transform(recs, ScoredIds.idFunction()),