@Override
    public void execute(Runnable command) {
      tasks.add(command);
    }

    boolean hasNext() {
      return !tasks.isEmpty();
    }

    void runNext() {
      assertTrue("expected at least one task to run", hasNext());
      tasks.remove().run();
    }

    void runAll() {
      while (hasNext()) {
        runNext();
      }
    }
  }

  private FakeExecutor fakePool;

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is(sameClass(Integer.class)));

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is(sameClass(Number.class)));

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is(sameClass(Object.class)));

        assertThat(it.hasNext(), is(not(true)));
    }

    /**

          int i;

          @Override
          public boolean hasNext() {
            return i < array.length;
          }

          @Override
          public String next() {
            if (!hasNext()) {
              throw new NoSuchElementException();
            }
            return array[i++];
          }
        };

    assertTrue(iterator.hasNext());
    assertEquals("a", iterator.next());
    try {

    Iterator<Subscriber> empty = registry.getSubscribers("");
    assertFalse(empty.hasNext());

    empty = registry.getSubscribers("");

    registry.register(s1);
    assertFalse(empty.hasNext());

    Iterator<Subscriber> one = registry.getSubscribers("");
    assertEquals(s1, one.next().target);
    assertFalse(one.hasNext());

    one = registry.getSubscribers("");

    registry.register(s2);

   * there are no elements left in the iteration. Failure to do so could result in an infinite loop.
   *
   * <p>The initial invocation of {@link #hasNext()} or {@link #next()} calls this method, as does
   * the first invocation of {@code hasNext} or {@code next} following each successful call to
   * {@code next}. Once the implementation either invokes {@code endOfData} or throws an exception,

        assertNotNull(iterator);
        assertTrue(iterator.hasNext());
        assertTrue(iterator.hasNext());
        Entry<String, String> entry = iterator.next();
        assertNotNull(entry);
        entry = iterator.next();
        assertNotNull(entry);
        assertThrows(NoSuchElementException.class, () -> iterator.next());
        assertFalse(iterator.hasNext());
    }

  }

  public void testOf_one() {
    Iterable<String> iterable = MinimalIterable.of("a");
    Iterator<String> iterator = iterable.iterator();
    assertTrue(iterator.hasNext());
    assertEquals("a", iterator.next());
    assertFalse(iterator.hasNext());
    try {
      iterator.next();
      fail();
    } catch (NoSuchElementException expected) {
    }
    try {
      iterable.iterator();
      fail();

  public Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  @CheckForNull
  public Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  @CheckForNull
  public Entry<E> pollFirstEntry() {

     */
    @Test
    public void testHasNext() {
        final ArrayIterator<String> itr = new ArrayIterator<String>("A", "B");
        assertThat(itr.hasNext(), is(true));
        itr.next();
        assertThat(itr.hasNext(), is(true));
        itr.next();
        assertThat(itr.hasNext(), is(not(true)));
    }

    /**
     * @throws Exception
     */
    @Test
    public void testRemove() throws Exception {

   * and updates {@link #successorIterator} to iterate through the successors of {@link #node}.
   */
  final boolean advance() {
    checkState(!successorIterator.hasNext());
    if (!nodeIterator.hasNext()) {
      return false;
    }
    node = nodeIterator.next();
    successorIterator = graph.successors(node).iterator();
    return true;
  }

  /**