assertThat(immutableValueGraph).isNotEqualTo(mutableValueGraph);
  }

  @Test
  public void copyOfImmutableValueGraph_optimized() {
    ValueGraph<String, Integer> graph1 =
        ImmutableValueGraph.copyOf(ValueGraphBuilder.directed().<String, Integer>build());
    ValueGraph<String, Integer> graph2 = ImmutableValueGraph.copyOf(graph1);

    assertThat(graph2).isSameInstanceAs(graph1);
  }

  @Test

 * }
 *
 * you will invoke it depending on the graph representation you're using.
 *
 * <p>If you have an instance of one of the primary {@code common.graph} types ({@link Graph},
 * {@link ValueGraph}, and {@link Network}):
 *
 * {@snippet :
 * someGraphAlgorithm(startNode, graph);
 * }
 *
 * This works because those types each implement {@code PredecessorsFunction}. It will also work

 * limitations under the License.
 */

package com.google.common.graph;

import java.util.Set;

/**
 * A non-public interface for the methods shared between {@link Graph}, {@link ValueGraph}, and
 * {@link Network}.
 *
 * @author Joshua O'Madadhain
 * @param <N> Node parameter type
 */
interface ArchetypeGraph<N> extends SuccessorsFunction<N>, PredecessorsFunction<N> {
  //

    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.directed().build();
    valueGraph.putEdgeValue("a", "b", 11);

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

  @Test
  public void forTree_withUndirectedValueGraph_throws() throws Exception {
    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.undirected().build();
    valueGraph.putEdgeValue("a", "b", 11);

  static final String ENDPOINTS_MISMATCH =
      "Mismatch: endpoints' ordering is not compatible with directionality of the graph";

  /** Singleton edge value for {@link Graph} implementations backed by {@link ValueGraph}s. */
  enum Presence {
    EDGE_EXISTS
  }

  public void copyOf_directedValueGraph() {
    ValueGraph<Integer, String> directedGraph = buildDirectedValueGraph();

    ValueGraph<Integer, String> copy = copyOf(directedGraph);
    assertThat(copy).isEqualTo(directedGraph);
  }

  @Test
  public void copyOf_undirectedValueGraph() {
    ValueGraph<Integer, String> undirectedGraph = buildUndirectedValueGraph();

    ValueGraph<Integer, String> copy = copyOf(undirectedGraph);

      public Graph<N> asGraph() {
        if (AbstractBaseGraph.this instanceof Graph) {
          return (Graph<N>) AbstractBaseGraph.this;
        } else if (AbstractBaseGraph.this instanceof ValueGraph) {
          return ((ValueGraph<N, ?>) AbstractBaseGraph.this).asGraph();
        }
        throw new UnsupportedOperationException(
            "Unexpected graph type: " + AbstractBaseGraph.this.getClass());
      }

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import org.jspecify.annotations.Nullable;

/**
 * Standard implementation of {@link ValueGraph} that supports the options supplied by {@link
 * AbstractGraphBuilder}.
 *
 * <p>This class maintains a map of nodes to {@link GraphConnections}.
 *

   *
   * <p>{@code incidentEdgeOrder(ElementOrder.stable())} guarantees the ordering of the returned
   * collections of the following methods:
   *
   * <ul>
   *   <li>For {@link Graph} and {@link ValueGraph}:
   *       <ul>
   *         <li>{@code edges()}: Stable order
   *         <li>{@code adjacentNodes(node)}: Connecting edge insertion order
   *         <li>{@code predecessors(node)}: Connecting edge insertion order

   *
   * <p>{@code incidentEdgeOrder(ElementOrder.stable())} guarantees the ordering of the returned
   * collections of the following methods:
   *
   * <ul>
   *   <li>For {@link Graph} and {@link ValueGraph}:
   *       <ul>
   *         <li>{@code edges()}: Stable order
   *         <li>{@code adjacentNodes(node)}: Connecting edge insertion order
   *         <li>{@code predecessors(node)}: Connecting edge insertion order