FoldedTreeSet implements SortedSet<E> { @Override public int size() { return size; } FoldedTreeSet();  FoldedTreeSet(Comparator<E> comparator); @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(); @Override int size(); @Override boolean isEmpty(); E get(Object obj, Comparator<?> cmp); E get(E entry); @Override @SuppressWarnings("unchecked") boolean contains(Object obj); @Override Iterator<E> iterator(); @Override Object[] toArray(); @Override @SuppressWarnings("unchecked") T[] toArray(T[] a); E addOrReplace(E entry); @Override boolean add(E entry); boolean addSortedLast(E entry); E removeAndGet(Object obj, Comparator<?> cmp); E removeAndGet(Object obj); boolean remove(Object obj, Comparator<?> cmp); @Override boolean remove(Object obj); @Override boolean containsAll(Collection<?> c); @Override boolean addAll(Collection<? extends E> c); @Override boolean retainAll(Collection<?> c); @Override boolean removeAll(Collection<?> c); @Override void clear(); double fillRatio(); boolean compact(long timeout);  }
@Test public void testSize() { FoldedTreeSet<String> instance = new FoldedTreeSet<>(); String entry = "apa"; assertEquals(0, instance.size()); instance.add(entry); assertEquals(1, instance.size()); instance.remove(entry); assertEquals(0, instance.size()); }