* @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsSelfLoops()}
   */
  @CanIgnoreReturnValue
  boolean putEdge(N nodeU, N nodeV);

  /**
   * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
   * endpoints}) if one is not already present.
   *

        .build();
  }

  @Override
  final void addNode(Integer n) {
    graphAsMutableGraph.addNode(n);
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphAsMutableGraph.putEdge(n1, n2);
  }

   * @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsSelfLoops()}
   */
  @CanIgnoreReturnValue
  boolean putEdge(N nodeU, N nodeV);

  /**
   * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
   * endpoints}) if one is not already present.
   *

        GraphBuilder.directed().<String>immutable().putEdge("A", "B").build();

    assertThat(graph.nodes()).containsExactly("A", "B");
    assertThat(graph.edges()).containsExactly(EndpointPair.ordered("A", "B"));
  }

  @Test
  public void immutableGraphBuilder_putEdgeFromEndpointPair() {
    ImmutableGraph<String> graph =
        GraphBuilder.directed().<String>immutable().putEdge(EndpointPair.ordered("A", "B")).build();

        GraphBuilder.directed().<String>immutable().putEdge("A", "B").build();

    assertThat(graph.nodes()).containsExactly("A", "B");
    assertThat(graph.edges()).containsExactly(EndpointPair.ordered("A", "B"));
  }

  @Test
  public void immutableGraphBuilder_putEdgeFromEndpointPair() {
    ImmutableGraph<String> graph =
        GraphBuilder.directed().<String>immutable().putEdge(EndpointPair.ordered("A", "B")).build();

        graph.addNode(gen.nextInt(NODE_POOL_SIZE));
      }
      ArrayList<Integer> nodeList = new ArrayList<>(graph.nodes());
      while (graph.edges().size() < NUM_EDGES) {
        graph.putEdge(getRandomElement(nodeList, gen), getRandomElement(nodeList, gen));
      }
      ArrayList<EndpointPair<Integer>> edgeList = new ArrayList<>(graph.edges());

      assertThat(graph.nodes()).hasSize(NUM_NODES);