Iterable<Character> result = Traverser.forGraph(TWO_TREES).depthFirstPreOrder('a');

    assertEqualCharNodes(result, "ab");
  }

  @Test
  public void forGraph_depthFirstPreOrderIterable_twoTrees() {
    assertEqualCharNodes(Traverser.forGraph(TWO_TREES).depthFirstPreOrder(charactersOf("a")), "ab");
    assertEqualCharNodes(
        Traverser.forGraph(TWO_TREES).depthFirstPreOrder(charactersOf("ac")), "abcd");
  }

    Iterable<Character> result = Traverser.forGraph(TWO_TREES).depthFirstPreOrder('a');

    assertEqualCharNodes(result, "ab");
  }

  @Test
  public void forGraph_depthFirstPreOrderIterable_twoTrees() {
    assertEqualCharNodes(Traverser.forGraph(TWO_TREES).depthFirstPreOrder(charactersOf("a")), "ab");
    assertEqualCharNodes(
        Traverser.forGraph(TWO_TREES).depthFirstPreOrder(charactersOf("ac")), "abcd");
  }

  public static <N> Traverser<N> forTree(SuccessorsFunction<N> tree) {
    if (tree instanceof BaseGraph) {
      checkArgument(((BaseGraph<?>) tree).isDirected(), "Undirected graphs can never be trees.");
    }
    if (tree instanceof Network) {
      checkArgument(((Network<?, ?>) tree).isDirected(), "Undirected networks can never be trees.");
    }
    return new Traverser<N>(tree) {
      @Override
      Traversal<N> newTraversal() {

import java.util.Deque;
import java.util.Iterator;
import java.util.Queue;
import javax.annotation.CheckForNull;

/**
 * Views elements of a type {@code T} as nodes in a tree, and provides methods to traverse the trees
 * induced by this traverser.
 *
 * <p>For example, the tree
 *
 * <pre>{@code
 *        h
 *      / | \
 *     /  e  \
 *    d       g
 *   /|\      |
 *  / | \     f
 * a  b  c
 * }</pre>
 *

  static final Tree c = new Tree('c');
  static final Tree d = new Tree('d', a, b, c);
  static final Tree e = new Tree('e');
  static final Tree f = new Tree('f');
  static final Tree g = new Tree('g', f);
  static final Tree h = new Tree('h', d, e, g);

  static String iterationOrder(Iterable<? extends Node> iterable) {
    StringBuilder builder = new StringBuilder();
    for (Node t : iterable) {

    tree.put("tree", 3);
    assertThat(tree.keySet()).containsExactly("tree", "google").inOrder();
    assertThat(tree.get("google")).containsExactly(6, 2).inOrder();

    TreeMultimap<String, Integer> copy = TreeMultimap.create(tree);
    assertEquals(tree, copy);
    assertThat(copy.keySet()).containsExactly("google", "tree").inOrder();
    assertThat(copy.get("google")).containsExactly(2, 6).inOrder();

  }

  private class ThreadedService extends AbstractService {
    final CountDownLatch hasConfirmedIsRunning = new CountDownLatch(1);

    /*
     * The main test thread tries to stop() the service shortly after
     * confirming that it is running. Meanwhile, the service itself is trying
     * to confirm that it is running. If the main thread's stop() call happens

  }

  /**
   * Returns the Method that can be used to return the size of a stack, or null if that method
   * cannot be found (it is only to be found in fairly recent JDKs). Tries to test method {@link
   * sun.misc.JavaLangAccess#getStackTraceDepth(Throwable) getStackTraceDepth} prior to return it
   * (might fail some JDKs).
   *

  }

  /**
   * Returns the Method that can be used to return the size of a stack, or null if that method
   * cannot be found (it is only to be found in fairly recent JDKs). Tries to test method {@link
   * sun.misc.JavaLangAccess#getStackTraceDepth(Throwable) getStackTraceDepth} prior to return it
   * (might fail some JDKs).
   *

        if (result == 0) {
          return count(getElement());
        } else {
          return result;
        }
      }
    };
  }

  /** Returns the first node in the tree that is in range. */
  @CheckForNull
  private AvlNode<E> firstNode() {
    AvlNode<E> root = rootReference.get();
    if (root == null) {
      return null;
    }
    AvlNode<E> node;