* Called after {@link #successorIterator} is exhausted. Advances {@link #node} to the next node
   * 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;
  }

  // First pass: filters out the entries of the slices.
  std::unordered_set<string> filtered_keys;
  BundleEntryProto entry;
  v2_reader_->Seek(kHeaderEntryKey);
  for (v2_reader_->Next(); v2_reader_->Valid(); v2_reader_->Next()) {
    CHECK(entry.ParseFromArray(v2_reader_->value().data(),
                               v2_reader_->value().size()))
        << entry.InitializationErrorString();

  private int position;

  /** Returns the element with the specified index. This method is called by {@link #next()}. */
  @ParametricNullness
  protected abstract E get(int index);

  /**
   * Constructs an iterator across a sequence of the given size whose initial position is 0. That
   * is, the first call to {@link #next()} will return the first element (or throw {@link
   * NoSuchElementException} if {@code size} is zero).
   *

     * stack so that it is returned by the next call to {@link Iterator#next()}. If the element is
     * not in {@link #nextElements}, this method throws an {@link UnknownElementException}.
     *
     * <p>This method is used when testing iterators without a known ordering. We poll the target
     * iterator's next element and pass it to the reference iterator through this method so it can

        while (properties.hasNext()) {
            Map.Entry property = (Map.Entry) properties.next();
            String key = (String) property.getKey();
            StringBuffer value = new StringBuffer();
            Iterator values = ((List) property.getValue()).iterator();
            while (values.hasNext()) {
                value.append(values.next());
                if (values.hasNext()) value.append(", ");
            }

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is("Foo"));

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is("Bar"));

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is("Baz"));

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

      int initialSize = map.size();
      boolean didRemove = entrySet.remove(entrySet.iterator().next());
      assertTrue(didRemove);
      assertEquals(initialSize - 1, map.size());
    } else {
      assertThrows(
          UnsupportedOperationException.class, () -> entrySet.remove(entrySet.iterator().next()));
    }
    assertInvariants(map);
  }

  public void testEntrySetRemoveMissingKey() {

 *       next task will wait for any running callable (or pending {@code Future} returned by an
 *       {@code AsyncCallable}) to complete, without interrupting it (and without calling {@code
 *       cancel} on the {@code Future}). So beware: <i>Even if you cancel every preceding {@code
 *       Future} returned by this class, the next task may still have to wait.</i>.

                    }

                    @Override
                    public Entry<String, String> next() {
                      return transform(iterator.next());
                    }

                    private Entry<String, String> transform(final Entry<String, String> next) {
                      return new Entry<String, String>() {

                        @Override

     */
    @Test
    public void testEntrySet() throws Exception {
        Iterator<Map.Entry<String, String>> i = map.entrySet().iterator();
        assertThat(i.next().getKey(), is(nullValue()));
        assertThat(i.next().getKey(), is("1"));
        assertThat(i.next().getKey(), is("2"));
    }

    /**
     * Test method for {@link org.seasar.util.collection.ArrayIterator#remove()}
     * .
     */
    @Test