throw new AssertionError("should never be called");
    }

    @Override
    Set<Entry<E>> createEntrySet() {
      return Sets.filter(unfiltered.entrySet(), entry -> predicate.apply(entry.getElement()));
    }

    @Override
    Iterator<Entry<E>> entryIterator() {
      throw new AssertionError("should never be called");
    }

    @Override

      throw new AssertionError("should never be called");
    }

    @Override
    Set<Entry<E>> createEntrySet() {
      return Sets.filter(unfiltered.entrySet(), entry -> predicate.apply(entry.getElement()));
    }

    @Override
    Iterator<Entry<E>> entryIterator() {
      throw new AssertionError("should never be called");
    }

    @Override

              }
            };
          }
        },
        "HashMap w/out null values",
        ALLOWS_NULL_KEYS);
  }

  /**
   * Map generator that verifies that {@code setUp()} methods are called in all the test cases. The
   * {@code setUpRan} parameter is set true by the {@code setUp} that every test case is supposed to
   * have registered, and set false by the {@code tearDown}. We use a dynamic proxy to intercept all

    return eventBus;
  }

  /** Returns the event object that caused the subscriber to throw. */
  public Object getEvent() {
    return event;
  }

  /** Returns the object context that the subscriber was called on. */
  public Object getSubscriber() {
    return subscriber;
  }

  /** Returns the subscribed method that threw the exception. */
  public Method getSubscriberMethod() {
    return subscriberMethod;
  }

   * {@code x}. This must not be called on a vertical transformation (i.e. when {@link
   * #isVertical()} is true).
   */
  public abstract double slope();

  /**
   * Returns the {@code y} corresponding to the given {@code x}. This must not be called on a
   * vertical transformation (i.e. when {@link #isVertical()} is true).
   */

 * family. <b>Avoid</b> creating a mock or stub {@code Future}. Mock and stub implementations are
 * fragile because they assume that only certain methods will be called and because they often
 * implement subtleties of the API improperly.
 *
 * <p><b>Custom implementation</b>: Avoid implementing {@code ListenableFuture} from scratch. If you

     */
    final Stack<E> previousElements = new Stack<>();

    /**
     * {@link #nextElements} if {@code next()} was called more recently then {@code previous},
     * {@link #previousElements} if the reverse is true, or -- overriding both of these -- {@code
     * null} if {@code remove()} or {@code add()} has been called more recently than either. We use
     * this to determine which stack to pop from on a call to {@code remove()} (or to pop from and

   * this graph.
   *
   * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}.
   *
   * <p>If {@code node} is removed from the graph after this method is called, the {@code Set}
   * {@code view} returned by this method will be invalidated, and will throw {@code
   * IllegalStateException} if it is accessed in any way, with the following exceptions:
   *
   * <ul>

 * instance contains a list of listeners, each with an associated {@code Executor}, and guarantees
 * that every {@code Runnable} that is {@linkplain #add added} will be executed after {@link
 * #execute()} is called. Any {@code Runnable} added after the call to {@code execute} is still
 * guaranteed to execute. There is no guarantee, however, that listeners will be executed in the
 * order that they are added.
 *

 * controls the order in which events are dispatched, while the executor controls how (i.e. on which
 * thread) the subscriber is actually called when an event is dispatched to it.
 *
 * @author Colin Decker
 */
abstract class Dispatcher {

  /**
   * Returns a dispatcher that queues events that are posted reentrantly on a thread that is already