### Question:
EmptyIntSet extends AbstractImmutableIntSet { @Override public boolean equals(Object obj) { if (obj instanceof Set) { return ((Set) obj).size() == 0; } return false; }  static IntSet getInstance(); @Override boolean contains(int i); @Override boolean containsAll(IntSet set); @Override int size(); @Override boolean isEmpty(); @Override boolean contains(Object o); @Override PrimitiveIterator.OfInt iterator(); @Override Object[] toArray(); @Override T[] toArray(T[] a); @Override boolean containsAll(Collection<?> c); @Override IntStream intStream(); @Override boolean equals(Object obj); @Override String toString();  }### Answer:
@Test public void testEquals() throws Exception { IntSet sis2 = new SingletonIntSet(4); assertNotEquals(es, sis2); assertNotEquals(sis2, es); IntSet sis3 = new SmallIntSet(2); assertEquals(sis3, es); assertEquals(es, sis3); }