return Graphs.transitiveClosure(graph);
  }

  @SuppressWarnings("PreferredInterfaceType")
  public static <N> Set<N> reachableNodes(Graph<N> graph, N node) {
    return Graphs.reachableNodes(graph, node);
  }

        }

        if (graph.isEmpty()) {
            throw new GraphConflictResolutionException("graph with an entry, but not vertices do not exist");
        }

        if (graph.isEmptyEdges()) {
            return null; // no edges - nothing to worry about
        }

        final TreeSet<MetadataGraphVertex> vertices = graph.getVertices();

        try {
            // edge case - single vertex graph

 * under the License.
 */
package org.apache.maven.graph;

import org.apache.maven.execution.MavenSession;
import org.apache.maven.execution.ProjectDependencyGraph;
import org.apache.maven.model.building.Result;

/**
 * Builds the {@link ProjectDependencyGraph inter-dependencies graph} between projects in the reactor.
 *
 * @since 3.0-alpha
 */
public interface GraphBuilder {

  static final String EDGE_NOT_IN_GRAPH = "Edge %s is not an element of this graph.";
  static final String NODE_REMOVED_FROM_GRAPH =
      "Node %s that was used to generate this set is no longer in the graph.";
  static final String NODE_PAIR_REMOVED_FROM_GRAPH =
      "Node %s or node %s that were used to generate this set are no longer in the graph.";
  static final String EDGE_REMOVED_FROM_GRAPH =

   * also connect {@code nodeV} to {@code nodeU}.
   *
   * <p>If this graph is directed, {@code edge} will be directed in this graph; if it is undirected,
   * {@code edge} will be undirected in this graph.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered.
   *
   * <p><b>{@code edge} must be unique to this graph</b>, just as a {@code Map} key must be. It must
   * also be non-null.
   *

    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");

    assertThrows(IllegalArgumentException.class, () -> Traverser.forTree(graph));
  }

  @Test
  @SuppressWarnings("CheckReturnValue")

    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");

    assertThrows(IllegalArgumentException.class, () -> Traverser.forTree(graph));
  }

  @Test
  @SuppressWarnings("CheckReturnValue")

import static org.junit.jupiter.api.Assertions.assertThrows;

public class GraphTest {

    @Test
    void testCycle() throws Graph.CycleDetectedException {
        Graph graph = new Graph();
        graph.addEdge("a1", "a2");
        assertThrows(Graph.CycleDetectedException.class, () -> graph.addEdge("a2", "a1"));
    }

    @Test
    public void testPerf() throws IOException {
        List<String[]> data = new ArrayList<>();

  Iterator<N> successorIterator = ImmutableSet.<N>of().iterator();

  static <N> EndpointPairIterator<N> of(BaseGraph<N> graph) {
    return graph.isDirected() ? new Directed<N>(graph) : new Undirected<N>(graph);
  }

  private EndpointPairIterator(BaseGraph<N> graph) {
    this.graph = graph;
    this.nodeIterator = graph.nodes().iterator();
  }

  /**

@Beta
@ElementTypesAreNonnullByDefault
public abstract class AbstractGraph<N> extends AbstractBaseGraph<N> implements Graph<N> {

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

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