network = builder.allowsSelfLoops(true).allowsParallelEdges(true).build();
    networkForTest = NetworkForTest.from(network);
  }

  @Test
  public void edgesConnecting_disconnectedNodes() {
    network.addNode(N1);
    network.addNode(N2);
    assertThat(networkForTest.edgesConnecting(N1, N2)).isEmpty();
  }

  @Test
  public void edgesConnecting_nodesNotInGraph() {