assertThat(graph.predecessors(N2)).containsExactly(N1);
    assertThat(graphAsMutableGraph.removeEdge(N1, N2)).isTrue();
    assertThat(graphAsMutableGraph.removeEdge(N1, N2)).isFalse();
    assertThat(graph.successors(N1)).isEmpty();
    assertThat(graph.predecessors(N2)).isEmpty();
  }

  @Test
  public void removeEdge_oneOfMany() {
    assume().that(graphIsMutable()).isTrue();

    putEdge(N1, N2);

    // for ug1, add e12 first, then e12_a
    g1.addEdge(N1, N2, E12);
    g1.addEdge(N1, N2, E12_A);

    // for ug2, add e12_a first, then e12
    g2.addEdge(N1, N2, E12_A);
    g2.addEdge(N1, N2, E12);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    network.addEdge(N1, N2, E12);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);

    // for ug1, add e12 first, then e12_a
    g1.addEdge(N1, N2, E12);
    g1.addEdge(N1, N2, E12_A);

    // for ug2, add e12_a first, then e12
    g2.addEdge(N1, N2, E12_A);
    g2.addEdge(N1, N2, E12);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    network.addEdge(N1, N2, E12);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);

    }
  }

  /** Returns the product of {@code n1} exclusive through {@code n2} inclusive. */
  @SuppressWarnings("UseCorrectAssertInTests") // TODO(b/345814817): Remove or convert assertion.
  private static BigInteger oldSlowFactorial(int n1, int n2) {
    assert n1 <= n2;
    if (IntMath.log2(n2, CEILING) * (n2 - n1) < Long.SIZE - 1) {
      // the result will definitely fit into a long
      long result = 1;

  }

  @Override
  final void addNode(Integer n) {
    graphBuilder.addNode(n);
    graph = graphBuilder.build();
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphBuilder.putEdge(n1, n2);
    graph = graphBuilder.build();
  }

  }

  @Override
  final void addNode(Integer n) {
    graphBuilder.addNode(n);
    graph = graphBuilder.build();
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphBuilder.putEdge(n1, n2);
    graph = graphBuilder.build();
  }

        .build();
  }

  @Override
  final void addNode(Integer n) {
    graphAsMutableGraph.addNode(n);
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphAsMutableGraph.putEdge(n1, n2);
  }

        .build();
  }

  @Override
  final void addNode(Integer n) {
    graphAsMutableGraph.addNode(n);
  }

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphAsMutableGraph.putEdge(n1, n2);
  }

        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }

        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }