Directory dir2 = getDir2(random);
ParallelReader pr = new ParallelReader();
pr.add(IndexReader.open(dir1, false));
pr.add(IndexReader.open(dir2, false));
Document doc11 = pr.document(0, new MapFieldSelector(new String[] {"f1"}));
Document doc24 = pr.document(1, new MapFieldSelector(Arrays.asList(new String[] {"f4"})));
Document doc223 = pr.document(1, new MapFieldSelector(new String[] {"f2", "f3"}));
assertEquals(1, doc11.getFields().size());
assertEquals(1, doc24.getFields().size());
assertEquals(2, doc223.getFields().size());