* 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

    if (supportsRemove) {
      int initialSize = map.size();
      boolean didRemove = entrySet.remove(entrySet.iterator().next());
      assertTrue(didRemove);
      assertEquals(initialSize - 1, map.size());
    } else {
      try {
        entrySet.remove(entrySet.iterator().next());
        fail("Expected UnsupportedOperationException.");
      } catch (UnsupportedOperationException expected) {
      }
    }

    checkNotNull(predicate);
    Iterator<T> iterator = removeFrom.iterator();
    while (iterator.hasNext()) {
      T next = iterator.next();
      if (predicate.apply(next)) {
        iterator.remove();
        return next;
      }
    }
    return null;
  }

  /**
   * Determines whether two iterables contain equal elements in the same order. More specifically,

        AvlNode<E> next = current.succ();

        current.elemCount = 0;
        // Also clear these fields so that one deleted Entry doesn't retain all elements.
        current.left = null;
        current.right = null;
        current.pred = null;
        current.succ = null;

        current = next;
      }
      successor(header, header);

   * high 32 bits of each long is the "prev" pointer, whereas the low 32 bits is the "succ" pointer
   * (pointing to the next entry in the linked list). The pointers in [size(), entries.length) are
   * all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "next" pointer equal to {@code ENDPOINT} is the last node.
   */

      // also be recursive and create StackOverflowErrors
      future.afterDone();
      // push the current set of listeners onto next
      next = future.clearListeners(next);
      future = null;
      while (next != null) {
        Listener curr = next;
        next = next.next;
        /*
         * requireNonNull is safe because the listener stack never contains TOMBSTONE until after
         * clearListeners.

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.SortedLists.KeyAbsentBehavior.NEXT_HIGHER;
import static com.google.common.collect.SortedLists.KeyAbsentBehavior.NEXT_LOWER;
import static com.google.common.collect.SortedLists.KeyPresentBehavior.ANY_PRESENT;
import static java.util.Objects.requireNonNull;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.SortedLists.KeyAbsentBehavior.NEXT_HIGHER;
import static com.google.common.collect.SortedLists.KeyAbsentBehavior.NEXT_LOWER;
import static com.google.common.collect.SortedLists.KeyPresentBehavior.ANY_PRESENT;
import static java.util.Objects.requireNonNull;

import com.google.common.annotations.Beta;

    assertEquals(0, (int) iter.next());

    // verify idempotence of hasNext()
    assertTrue(iter.hasNext());
    assertTrue(iter.hasNext());
    assertTrue(iter.hasNext());
    assertEquals(1, (int) iter.next());

    assertFalse(iter.hasNext());

    // Make sure computeNext() doesn't get invoked again
    assertFalse(iter.hasNext());

    try {
      iter.next();
      fail("no exception thrown");

    final String keyToRemove;
    try {
      map = makePopulatedMap();
    } catch (UnsupportedOperationException e) {
      return;
    }
    keyToRemove = map.keySet().iterator().next();
    if (supportsRemove) {
      int initialSize = map.size();
      map.get(keyToRemove);
      map.remove(keyToRemove);
      // This line doesn't hold - see the Javadoc comments above.