@Test
public void testEstimatePref() throws Exception {

  DataModel dataModel = getDataModel(
          new long[] {1, 2, 3, 4},
          new Double[][] {
                  {0.1, 0.3},
                  {0.2, 0.3, 0.3},
                  {0.4, 0.3, 0.5},
                  {0.7, 0.3, 0.8, 0.9},
          });
  UserSimilarity similarity = new PearsonCorrelationSimilarity(dataModel);
  ClusterSimilarity clusterSimilarity = new FarthestNeighborClusterSimilarity(similarity);
  Recommender recommender = new TreeClusteringRecommender2(dataModel, clusterSimilarity, 2);
  assertEquals(0.9f, recommender.estimatePreference(3, 3), EPSILON);
}