### Question:
WeakSet implements Iterable<T> { public abstract void clear(); WeakSet(); abstract void add(T t); abstract void remove(T t); abstract boolean contains(T t); abstract void clear(); abstract int size(); abstract boolean isEmpty(); abstract Collection<T> values(); Stream<T> stream(); @Override String toString();  }### Answer:
@Test public void testClear() { WeakSet<String> weakSet = WeakDataStructureFactory.createCopyOnWriteWeakSet(); String[] values = { "one", "two", "three" }; for (String value : values) { weakSet.add(value); } assertTrue("The weak set does not contain the correct number of " + "elements after calling add().", (values.length == weakSet.size())); weakSet.clear(); assertTrue("The weak set does not have 0 elements after calling " + "clear().", (weakSet.size() == 0)); assertTrue("WeakSet.isEmpty() did not return true when the set is " + "empty.", weakSet.isEmpty()); }