ObservableSet { public boolean contains(T val) { return delegate.contains(val); } ObservableSet();  ObservableSet(Set<T> delegate); void addListener(CollectionChangeListener<? super T> listener); void removeListener(CollectionChangeListener<? super T> listener); boolean add(T val); boolean remove(T val); boolean contains(T val);  }
@Test public void testContains() { set.add("val1"); assertTrue(set.contains("val1")); set.remove("val1"); assertFalse(set.contains("val1")); assertFalse(set.contains("different")); }