assertThat(network.edgesConnecting(N1, N1)).isEmpty();
    assertThat(network.edgesConnecting(N1, N2)).containsExactly(E12);
  }

  @Test
  public void concurrentIteration() throws Exception {
    addEdge(1, 2, "foo");
    addEdge(3, 4, "bar");
    addEdge(5, 6, "baz");

    int threadCount = 20;
    ExecutorService executor = newFixedThreadPool(threadCount);

        .containsExactly(
            EndpointPair.unordered(2, 3),
            EndpointPair.unordered(1, 2),
            EndpointPair.unordered(2, 4))
        .inOrder();
  }

  @Test
  public void concurrentIteration() throws Exception {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");
    graph.putEdgeValue(3, 4, "B");
    graph.putEdgeValue(5, 6, "C");

    int threadCount = 20;

        .containsExactly(
            EndpointPair.unordered(2, 3),
            EndpointPair.unordered(1, 2),
            EndpointPair.unordered(2, 4))
        .inOrder();
  }

  @Test
  public void concurrentIteration() throws Exception {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");
    graph.putEdgeValue(3, 4, "B");
    graph.putEdgeValue(5, 6, "C");

    int threadCount = 20;