@Test
  public void testLimitedView() throws IOException {
    File file = folder.newFile();
    FileChannel chan = new RandomAccessFile(file, "rw").getChannel();
    BinaryIndexTableWriter writer = BinaryIndexTableWriter.create(BinaryFormat.create(), chan, 3);
    writer.writeEntry(12, new int[] {0});
    writer.writeEntry(17, new int[] {1, 3});
    writer.writeEntry(19, new int[] {4, 5});

    MappedByteBuffer buffer = chan.map(FileChannel.MapMode.READ_ONLY, 0, chan.size());
    BinaryIndexTable tbl = BinaryIndexTable.fromBuffer(3, buffer);
    tbl = tbl.createLimitedView(2);
    assertThat(tbl.getKeys(), hasSize(2));
    assertThat(tbl.getKeys(), contains(12L, 17L));
    assertThat(tbl.getEntry(12), contains(0));
    assertThat(tbl.getEntry(17), contains(1));
    assertThat(tbl.getEntry(19), nullValue());
    assertThat(tbl.getEntry(-1), nullValue());

    BinaryIndexTable serializedTbl = SerializationUtils.clone(tbl);
    assertThat(serializedTbl.getKeys(), hasSize(2));
    assertThat(serializedTbl.getKeys(), contains(12L, 17L));
    assertThat(serializedTbl.getEntry(12), contains(0));
    assertThat(serializedTbl.getEntry(17), contains(1));
    assertThat(serializedTbl.getEntry(19), nullValue());
    assertThat(serializedTbl.getEntry(-1), nullValue());
  }
  /**
   * Write a user or item index to the file.
   *
   * @param map The index to write.
   */
  private void writeIndex(Long2ObjectMap<IntList> map) throws IOException {
    LongSortedSet keys = LongUtils.packedSet(map.keySet());
    BinaryIndexTableWriter tableWriter =
        BinaryIndexTableWriter.create(format, channel, keys.size());

    SortComparator indexComparator = new SortComparator();

    LongIterator iter = keys.iterator();
    while (iter.hasNext()) {
      final long key = iter.nextLong();
      int[] indexes = map.get(key).toIntArray();
      if (needsSorting) {
        IntArrays.quickSort(indexes, indexComparator);
      }

      if (translationMap != null) {
        for (int i = 0; i < indexes.length; i++) {
          indexes[i] = translationMap[indexes[i]];
        }
      }

      logger.debug("writing {} indices for id {}", key, indexes.length);
      tableWriter.writeEntry(key, indexes);
    }
  }
  @Test
  public void testSingleEntry() throws IOException {
    File file = folder.newFile();
    FileChannel chan = new RandomAccessFile(file, "rw").getChannel();
    BinaryIndexTableWriter w = BinaryIndexTableWriter.create(BinaryFormat.create(), chan, 1);
    w.writeEntry(42, new int[] {0});

    MappedByteBuffer buf = chan.map(FileChannel.MapMode.READ_ONLY, 0, chan.size());
    BinaryIndexTable tbl = BinaryIndexTable.fromBuffer(1, buf);
    assertThat(tbl.getKeys(), contains(42L));
    assertThat(tbl.getEntry(42), contains(0));
    assertThat(tbl.getEntry(43), nullValue());
  }