* graph.putEdge("bread", "bread");
 * graph.putEdge("chocolate", "peanut butter");
 * graph.putEdge("peanut butter", "jelly");
 *
 * // Building an immutable graph
 * ImmutableGraph<String> immutableGraph =
 *     GraphBuilder.undirected()
 *         .allowsSelfLoops(true)
 *         .<String>immutable()
 *         .putEdge("bread", "bread")
 *         .putEdge("chocolate", "peanut butter")

    return graphBuilder.build();
  }

  @Override
  final void addNode(Integer n) {
    graphBuilder.addNode(n);
    graph = graphBuilder.build();
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphBuilder.putEdge(n1, n2);
    graph = graphBuilder.build();
  }

    undirectedGraph.putEdge(N2, N3);
    undirectedGraph.putEdge(N3, N4);

    MutableGraph<Integer> expectedClosure = GraphBuilder.undirected().allowsSelfLoops(true).build();
    expectedClosure.putEdge(N1, N1);
    expectedClosure.putEdge(N1, N2);
    expectedClosure.putEdge(N1, N3);
    expectedClosure.putEdge(N1, N4);
    expectedClosure.putEdge(N2, N2);
    expectedClosure.putEdge(N2, N3);
    expectedClosure.putEdge(N2, N4);

   * insertion order.
   */
  private void populateStarShapedGraph() {
    putEdge(2, 1);
    putEdge(1, 4);
    putEdge(1, 3);
    putEdge(5, 1);
    putEdge(1, 2);
    putEdge(3, 1);
  }

  // Element Mutation

  @Test
  public void putEdge_existingNodes() {
    assume().that(graphIsMutable()).isTrue();

    g1.putEdge(N1, N2);
    g1.putEdge(N3, N1);

    // for g2, add 3->1 first, then 1->2
    g2.putEdge(N3, N1);
    g2.putEdge(N1, N2);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    graph.putEdge(N1, N2);

    MutableGraph<Integer> g2 = createGraph(edgeType);
    g2.putEdge(N2, N1);

    switch (edgeType) {

    MutableGraph<Integer> directedGraph = GraphBuilder.directed().allowsSelfLoops(true).build();
    directedGraph.addNode(N0);
    directedGraph.putEdge(N1, N2);
    directedGraph.putEdge(N2, N1);
    directedGraph.putEdge(N1, N3);
    directedGraph.putEdge(N4, N4);
    containsExactlySanityCheck(
        directedGraph.edges(),
        EndpointPair.ordered(N1, N2),
        EndpointPair.ordered(N2, N1),

    MutableGraph<Integer> directedGraph = GraphBuilder.directed().allowsSelfLoops(true).build();
    directedGraph.addNode(N0);
    directedGraph.putEdge(N1, N2);
    directedGraph.putEdge(N2, N1);
    directedGraph.putEdge(N1, N3);
    directedGraph.putEdge(N4, N4);
    containsExactlySanityCheck(
        directedGraph.edges(),
        EndpointPair.ordered(N1, N2),
        EndpointPair.ordered(N2, N1),

    assume().that(graphIsMutable()).isTrue();

    putEdge(N1, N2);
    putEdge(N1, N3);
    putEdge(N1, N4);
    assertThat(graphAsMutableGraph.removeEdge(N1, N3)).isTrue();
    assertThat(graph.adjacentNodes(N1)).containsExactly(N2, N4);
  }

  @Test
  public void removeEdge_nodeNotPresent() {
    assume().that(graphIsMutable()).isTrue();

    putEdge(N1, N2);

   *
   * <pre>{@code
   * static final ImmutableGraph<Country> COUNTRY_ADJACENCY_GRAPH =
   *     GraphBuilder.undirected()
   *         .<Country>immutable()
   *         .putEdge(FRANCE, GERMANY)
   *         .putEdge(FRANCE, BELGIUM)
   *         .putEdge(GERMANY, BELGIUM)
   *         .addNode(ICELAND)
   *         .build();
   * }</pre>
   *

    return graphBuilder.build();
  }

  @Override
  final void addNode(Integer n) {
    graphBuilder.addNode(n);
    graph = graphBuilder.build();
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphBuilder.putEdge(n1, n2);
    graph = graphBuilder.build();
  }