* {@snippet :
 * public class SafeBox<V> {
 *   private V value;
 *   private final Monitor monitor = new Monitor();
 *   private final Monitor.Guard valuePresent = monitor.newGuard(() -> value != null);
 *   private final Monitor.Guard valueAbsent = monitor.newGuard(() -> value == null);
 *
 *   public V get() throws InterruptedException {
 *     monitor.enterWhen(valuePresent);
 *     try {
 *       V result = value;

    TestGuard guard = new TestGuard(true);
    thread1.callAndAssertReturns(enterWhen(), guard);
    // same as above but with the new syntax
    thread1.callAndAssertReturns(enterWhen(), monitor.newGuard(() -> true));
  }

  public final void testEnterWhen_initiallyFalse() throws Exception {
    TestGuard guard = new TestGuard(false);
    thread1.callAndAssertWaits(enterWhen(), guard);
    monitor.enter();