@Test
public void lessItemsThanBatchSize() throws Exception {

  FastByIDMap<PreferenceArray> userData = new FastByIDMap<>();
  userData.put(1, new GenericUserPreferenceArray(Arrays.asList(new GenericPreference(1, 1, 1),
      new GenericPreference(1, 2, 1), new GenericPreference(1, 3, 1))));
  userData.put(2, new GenericUserPreferenceArray(Arrays.asList(new GenericPreference(2, 1, 1),
      new GenericPreference(2, 2, 1), new GenericPreference(2, 4, 1))));
  DataModel dataModel = new GenericDataModel(userData);
  ItemBasedRecommender recommender =
      new GenericItemBasedRecommender(dataModel, new TanimotoCoefficientSimilarity(dataModel));
  BatchItemSimilarities batchSimilarities = new MultithreadedBatchItemSimilarities(recommender, 10);
  batchSimilarities.computeItemSimilarities(1, 1, mock(SimilarItemsWriter.class));
}