*
 * <ul>
 *   <li>Test cases related to whether the graph is directed, undirected, mutable, or immutable.
 *   <li>Test cases related to the specific implementation of the {@link Network} interface.
 * </ul>
 *
 * TODO(user): Make this class generic (using <N, E>) for all node and edge types.
 * TODO(user): Differentiate between directed and undirected edge strings.
 */
public abstract class AbstractNetworkTest {

 *
 * <ul>
 *   <li>Test cases related to whether the graph is directed, undirected, mutable, or immutable.
 *   <li>Test cases related to the specific implementation of the {@link Network} interface.
 * </ul>
 *
 * TODO(user): Make this class generic (using <N, E>) for all node and edge types.
 * TODO(user): Differentiate between directed and undirected edge strings.
 */
public abstract class AbstractNetworkTest {

   * }</pre>
   *
   * @param tree {@link SuccessorsFunction} representing a directed acyclic graph that has at most
   *     one path between any two nodes
   */
  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) {

    MutableGraph<String> graph = GraphBuilder.directed().build();
    graph.putEdge("a", "b");

    Traverser.forTree(graph); // Does not throw
  }

  @Test
  public void forTree_withUndirectedGraph_throws() throws Exception {
    MutableGraph<String> graph = GraphBuilder.undirected().build();
    graph.putEdge("a", "b");

    MutableGraph<String> graph = GraphBuilder.directed().build();
    graph.putEdge("a", "b");

    Traverser.forTree(graph); // Does not throw
  }

  @Test
  public void forTree_withUndirectedGraph_throws() throws Exception {
    MutableGraph<String> graph = GraphBuilder.undirected().build();
    graph.putEdge("a", "b");

import static org.junit.Assert.assertTrue;

import com.google.common.testing.EqualsTester;
import java.util.Set;
import org.junit.After;
import org.junit.Test;

/**
 * Abstract base class for testing undirected {@link Graph} implementations defined in this package.
 */
public abstract class AbstractStandardUndirectedGraphTest extends AbstractGraphTest {

  @After
  public void validateUndirectedEdges() {

import static org.junit.Assert.assertTrue;

import com.google.common.testing.EqualsTester;
import java.util.Set;
import org.junit.After;
import org.junit.Test;

/**
 * Abstract base class for testing undirected {@link Graph} implementations defined in this package.
 */
public abstract class AbstractStandardUndirectedGraphTest extends AbstractGraphTest {

  @After
  public void validateUndirectedEdges() {

import com.google.common.testing.EqualsTester;
import java.util.Optional;
import java.util.Set;
import org.junit.After;
import org.junit.Test;

/**
 * Abstract base class for testing undirected {@link Network} implementations defined in this
 * package.
 */
public abstract class AbstractStandardUndirectedNetworkTest extends AbstractNetworkTest {

import com.google.common.collect.ImmutableSet;
import com.google.common.testing.EqualsTester;
import java.util.Set;
import org.junit.After;
import org.junit.Test;

/**
 * Abstract base class for testing undirected {@link Network} implementations defined in this
 * package.
 */
public abstract class AbstractStandardUndirectedNetworkTest extends AbstractNetworkTest {

    return endpoints.isOrdered() == this.isDirected();
  }

  @Override
  public final boolean equals(@CheckForNull Object obj) {
    if (obj == this) {
      return true;
    }
    if (!(obj instanceof Network)) {
      return false;
    }
    Network<?, ?> other = (Network<?, ?>) obj;

    return isDirected() == other.isDirected()
        && nodes().equals(other.nodes())