/** @throws Exception Thrown if test failed. */
  public void testA() throws Exception {
    Collection<Integer> set = new GridConcurrentWeakHashSet<>();

    Integer i = 1;

    assert set.add(i);
    assert !set.add(i);

    assert set.contains(i);

    assert set.size() == 1;

    Collection<Integer> c = F.asList(2, 3, 4, 5);

    assert set.addAll(c);
    assert !set.addAll(c);

    assert set.containsAll(c);

    assert set.size() == 1 + c.size();

    assert set.remove(i);
    assert !set.remove(i);

    assert !set.contains(i);

    assert set.size() == c.size();

    assert set.removeAll(c);
    assert !set.removeAll(c);

    assert !set.containsAll(c);

    assert set.isEmpty();

    Collection<Integer> c1 = Arrays.asList(1, 3, 5, 7, 9);

    int cnt = 0;

    for (Iterator<Integer> iter = set.iterator(); iter.hasNext(); cnt++) c1.contains(iter.next());

    assert set.size() == cnt;

    assert set.size() == set.toArray().length;

    assert set.addAll(c1);

    assert set.retainAll(c);
    assert !set.retainAll(c);

    Collection<Integer> c2 = F.retain(c1, true, c);

    assert set.containsAll(c2);
    assert !set.containsAll(c1);
    assert !set.containsAll(c);

    assert set.size() == c2.size();

    set.clear();

    assert set.isEmpty();

    try {
      set.iterator().next();

      assert false;
    } catch (NoSuchElementException ignored) {
      assert true;
    }

    try {
      set.add(null);

      assert false;
    } catch (NullPointerException ignored) {
      assert true;
    }
  }