### Question:
ImmutableIntSet implements IntSet { public static ImmutableIntSet emptySet() { return EMPTY_SET; } ImmutableIntSet(Set<Integer> delegate); static ImmutableIntSet wrap(Set<Integer> delegate); static ImmutableIntSet emptySet(); @Override boolean contains(int element); @Override boolean containsAll(Collection<?> coll); @Override int size(); @Override boolean isEmpty(); @Override boolean contains(Object o); @NotNull @Override Object[] toArray(); @NotNull @Override T[] toArray(@NotNull T[] a); @Override int[] toIntArray(); @Override String toString(); @NotNull @Override Iterator<Integer> iterator(); @Override boolean add(int element); @Override boolean remove(int element); @Override boolean add(Integer integer); @Override boolean remove(Object o); @Override boolean addAll(@NotNull Collection<? extends Integer> c); @Override boolean retainAll(@NotNull Collection<?> c); @Override boolean removeAll(@NotNull Collection<?> c); @Override void clear(); @Override void forEach(Consumer<? super Integer> act); @Override boolean removeIf(Predicate<? super Integer> filter); @Override Spliterator<Integer> spliterator(); @Override Stream<Integer> stream(); @Override Stream<Integer> parallelStream();  }### Answer:
@Test public void emptySet() { ImmutableIntSet emptySet = ImmutableIntSet.emptySet(); assertTrue(emptySet.isEmpty()); assertThat(emptySet.size(), is(0)); }