}

  @Test
  public void edges_oneEdge() {
    addEdge(N1, N2, E12);
    assertThat(network.edges()).containsExactly(E12);
  }

  @Test
  public void edges_noEdges() {
    assertThat(network.edges()).isEmpty();
    // Network with no edges, given disconnected nodes
    addNode(N1);
    addNode(N2);
    assertThat(network.edges()).isEmpty();
  }

  @Test