addEdge(N1, N1, E11);
    addEdge(N1, N1, E11_A);

    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11, E11_A);
  }

  @Test
  public void hasEdgeConnecting_disconnectedNodes() {
    addNode(N1);
    addNode(N2);
    assertThat(network.hasEdgeConnecting(N1, N2)).isFalse();
  }

  @Test
  public void hasEdgesConnecting_nodesNotInGraph() {
    addNode(N1);