### Question:
BufferedFileBackedSortedSet implements SortedSet<E> { @Override public SortedSet<E> headSet(E toElement) { return set.headSet(toElement); } BufferedFileBackedSortedSet(BufferedFileBackedSortedSet<E> other);  BufferedFileBackedSortedSet(List<SortedSetFileHandlerFactory> handlerFactories);  BufferedFileBackedSortedSet(List<SortedSetFileHandlerFactory> handlerFactories, FileSortedSet.FileSortedSetFactory<E> setFactory);  BufferedFileBackedSortedSet(Comparator<? super E> comparator, List<SortedSetFileHandlerFactory> handlerFactories);  BufferedFileBackedSortedSet(Comparator<? super E> comparator, List<SortedSetFileHandlerFactory> handlerFactories,
                    FileSortedSet.FileSortedSetFactory<E> setFactory);  BufferedFileBackedSortedSet(Comparator<? super E> comparator, int bufferPersistThreshold, int maxOpenFiles, int numRetries,
                    List<SortedSetFileHandlerFactory> handlerFactories);  BufferedFileBackedSortedSet(Comparator<? super E> comparator, int bufferPersistThreshold, int maxOpenFiles, int numRetries,
                    List<SortedSetFileHandlerFactory> handlerFactories, FileSortedSet.FileSortedSetFactory<E> setFactory); void persist(); boolean hasPersistedData(); boolean isPersisted(); @Override int size(); int getBufferPersistThreshold(); int getBufferSize(); @Override boolean isEmpty(); @Override boolean contains(Object o); @Override boolean containsAll(Collection<?> c); @Override Iterator<E> iterator(); void compact(int maxFiles); @Override Object[] toArray(); @Override T[] toArray(T[] a); @Override boolean add(E e); @Override boolean addAll(Collection<? extends E> c); @Override boolean remove(Object o); @Override boolean retainAll(Collection<?> c); @Override boolean removeAll(Collection<?> c); @Override void clear(); @Override Comparator<? super E> comparator(); @Override SortedSet<E> subSet(E fromElement, E toElement); @Override SortedSet<E> headSet(E toElement); @Override SortedSet<E> tailSet(E fromElement); @Override E first(); @Override E last();  }### Answer:
@Test public void testHeadSet() { int end = sortedOrder.length / 3; try { SortedSet<byte[]> subSet = set.headSet(data[sortedOrder[end]]); SortedSet<byte[]> expected = new TreeSet<>(set.comparator()); for (int i = 0; i < end; i++) { expected.add(data[sortedOrder[i]]); } assertEquals(expected, subSet); } catch (Exception e) { } }