expectedClosure.putEdge(N1, N3);
    expectedClosure.putEdge(N1, N4);
    expectedClosure.putEdge(N2, N1);
    expectedClosure.putEdge(N2, N2);
    expectedClosure.putEdge(N2, N3);
    expectedClosure.putEdge(N2, N4);
    expectedClosure.putEdge(N3, N1);
    expectedClosure.putEdge(N3, N2);
    expectedClosure.putEdge(N3, N3);
    expectedClosure.putEdge(N3, N4);
    expectedClosure.putEdge(N4, N1);

   *
   * <pre>
   * Nodes = {N1, N2, N3, N4}
   *    N2           __
   *   /  \         |  |
   * N1----N3      N4__|
   *
   * Visited Nodes = {}
   * EndpointPair [N1, N2] - return
   * EndpointPair [N1, N3] - return
   * Visited Nodes = {N1}
   * EndpointPair [N2, N1] - skip
   * EndpointPair [N2, N3] - return
   * Visited Nodes = {N1, N2}
   * EndpointPair [N3, N1] - skip
   * EndpointPair [N3, N2] - skip

  @Test
  public void equivalent_connectionsDiffer() {
    network.addEdge(N1, N2, E12);
    network.addEdge(N1, N3, E13);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);
    // connect E13 to N1 and N2, and E12 to N1 and N3 => not equivalent
    g2.addEdge(N1, N2, E13);
    g2.addEdge(N1, N3, E12);

    assertThat(network).isNotEqualTo(g2);
  }

  @Test
  public void equivalent_connectionsDiffer() {
    network.addEdge(N1, N2, E12);
    network.addEdge(N1, N3, E13);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);
    // connect E13 to N1 and N2, and E12 to N1 and N3 => not equivalent
    g2.addEdge(N1, N2, E13);
    g2.addEdge(N1, N3, E12);

    assertThat(network).isNotEqualTo(g2);
  }

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n2{margin-top:-.5rem!important}.mr-n2,.mx-n2{margin-right:-.5rem!important}.mb-n2,.my-n2{margin-bottom:-.5rem!important}.ml-n2,.mx-n2{margin-left:-.5rem!important}.m-n3{margin:-1rem!important}.mt-n3,.my-n3{margin-top:-1rem!important}.mr-n3,.mx-n3{margin-right:-1rem!important}.mb-n3,.my-n3{margin-bottom:-1rem!important}.ml-n3,.mx-n3{margin-left:-1rem!important}.m-n4{margin:-1.5rem!important}.mt-n4,.my-n4{margin-top:-1.5rem!important}.mr-n4,.mx-n4{margin-right:-1.5rem!important}.mb-n4,.my-n4{margi...

    assertTrue(graphAsMutableGraph.putEdge(N4, N1));
    assertTrue(graphAsMutableGraph.putEdge(N2, N3));
    assertThat(graph.nodes()).containsExactly(N1, N5, N4, N2, N3).inOrder();
    assertThat(graph.adjacentNodes(N1)).containsExactly(N4, N5);
    assertThat(graph.adjacentNodes(N2)).containsExactly(N3);
    assertThat(graph.adjacentNodes(N3)).containsExactly(N2);
    assertThat(graph.adjacentNodes(N4)).containsExactly(N1);

    assertTrue(networkAsMutableNetwork.addEdge(N2, N3, E23));
    assertThat(network.nodes()).containsExactly(N1, N5, N4, N2, N3);
    assertThat(network.edges()).containsExactly(E15, E41, E23);
    assertThat(network.edgesConnecting(N1, N5)).containsExactly(E15);
    assertThat(network.edgesConnecting(N4, N1)).containsExactly(E41);
    assertThat(network.edgesConnecting(N2, N3)).containsExactly(E23);

    assertTrue(networkAsMutableNetwork.addEdge(N2, N3, E23));
    assertThat(network.nodes()).containsExactly(N1, N5, N4, N2, N3);
    assertThat(network.edges()).containsExactly(E15, E41, E23);
    assertThat(network.edgesConnecting(N1, N5)).containsExactly(E15);
    assertThat(network.edgesConnecting(N4, N1)).containsExactly(E41);
    assertThat(network.edgesConnecting(N2, N3)).containsExactly(E23);

  @Test
  public void adjacentEdges_bothEndpoints() {
    addEdge(N1, N2, E12);
    addEdge(N2, N3, E23);
    addEdge(N3, N1, E31);
    addEdge(N3, N4, E34);
    assertThat(network.adjacentEdges(E12)).containsExactly(E31, E23);
  }

  @Test
  public void adjacentEdges_noAdjacentEdges() {
    addEdge(N1, N2, E12);
    addEdge(N3, N4, E34);
    assertThat(network.adjacentEdges(E12)).isEmpty();
  }

  @Test