MutableGraph<Integer> undirectedGraph =
        GraphBuilder.undirected().allowsSelfLoops(false).build();
    undirectedGraph.putEdge(N1, N2);
    undirectedGraph.putEdge(N1, N3);
    undirectedGraph.putEdge(N2, N3);
    undirectedGraph.addNode(N4);

    MutableGraph<Integer> expectedClosure = GraphBuilder.undirected().allowsSelfLoops(true).build();
    expectedClosure.putEdge(N1, N1);

 *
 * <ul>
 *   <li>Test cases related to whether the graph is directed or undirected.
 *   <li>Test cases related to the specific implementation of the {@link Graph} 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 AbstractGraphTest {

  Graph<Integer> graph;

   *     false, creates an instance for graphs whose edges are each undirected.
   */
  AbstractGraphBuilder(boolean directed) {
    this.directed = directed;
  }

import com.google.common.collect.ImmutableList;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

/**
 * Standard implementation of {@link MutableNetwork} that supports both directed and undirected
 * graphs. Instances of this class should be constructed with {@link NetworkBuilder}.
 *
 * <p>Time complexities for mutation methods are all O(1) except for {@code removeNode(N node)},

    ImmutableValueGraph<String, Integer> emptyGraph =
        ValueGraphBuilder.directed()
            .allowsSelfLoops(true)
            .nodeOrder(ElementOrder.<String>natural())
            .<String, Integer>immutable()
            .build();

    assertThat(emptyGraph.isDirected()).isTrue();
    assertThat(emptyGraph.allowsSelfLoops()).isTrue();

  Network<Integer, String> undirectedNetwork;

  @Before
  public void init() {
    MutableGraph<Integer> mutableDirectedGraph =
        GraphBuilder.directed().allowsSelfLoops(true).build();
    MutableGraph<Integer> mutableUndirectedGraph =
        GraphBuilder.undirected().allowsSelfLoops(true).build();
    graphsToTest = ImmutableList.of(mutableDirectedGraph, mutableUndirectedGraph);
    directedGraph = mutableDirectedGraph;

    this.edgeCount = checkNonNegative(edgeCount);
  }

  @Override
  public Set<N> nodes() {
    return nodeConnections.unmodifiableKeySet();
  }

  @Override
  public boolean isDirected() {
    return isDirected;
  }

  @Override
  public boolean allowsSelfLoops() {
    return allowsSelfLoops;
  }

  @Override
  public ElementOrder<N> nodeOrder() {
    return nodeOrder;
  }

 * limitations under the License.
 */

package com.google.common.graph;

import com.google.common.graph.GraphConstants.Presence;

/**
 * Standard implementation of {@link MutableGraph} that supports both directed and undirected
 * graphs. Instances of this class should be constructed with {@link GraphBuilder}.
 *
 * <p>Time complexities for mutation methods are all O(1) except for {@code removeNode(N node)},

    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");