network.addEdge(N1, N1, E11);

    MutableNetwork<Integer, String> g2 = createNetwork(oppositeType(edgeType));
    g2.addEdge(N1, N1, E11);

    assertThat(network).isNotEqualTo(g2);
  }

  // Node/edge sets are the same, but node/edge connections differ.
  @Test
  public void equivalent_connectionsDiffer() {
    network.addEdge(N1, N2, E12);
    network.addEdge(N1, N3, E13);

    addEdge(N1, N1, E11);
    assertThat(network.degree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.degree(N1)).isEqualTo(3);
  }

  @Test
  public void inDegree_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.inDegree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.inDegree(N1)).isEqualTo(3);
  }

    addEdge(N1, N1, E11);
    assertThat(network.degree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.degree(N1)).isEqualTo(3);
  }

  @Test
  public void inDegree_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.inDegree(N1)).isEqualTo(1);
    addEdge(N4, N1, E41);
    assertThat(network.inDegree(N1)).isEqualTo(2);
  }

    directedGraph.putEdgeValue(N1, N1, E11);
    directedGraph.putEdgeValue(N3, N4, E34);

    MutableValueGraph<Integer, String> expectedTranspose =
        ValueGraphBuilder.directed().allowsSelfLoops(true).build();
    expectedTranspose.putEdgeValue(N3, N1, E13);
    expectedTranspose.putEdgeValue(N1, N3, E31);
    expectedTranspose.putEdgeValue(N2, N1, E12);
    expectedTranspose.putEdgeValue(N1, N1, E11);

    assertThat(graphAsMutableGraph.removeEdge(N1, N3)).isTrue();
    assertThat(graph.adjacentNodes(N1)).containsExactly(N2, N4);
  }

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

    putEdge(N1, N2);
    assertThat(graphAsMutableGraph.removeEdge(N1, NODE_NOT_IN_GRAPH)).isFalse();
    assertThat(graph.successors(N1)).contains(N2);
  }

  @Test

  public <N1 extends N, E1 extends E> MutableNetwork<N1, E1> build() {
    return new StandardMutableNetwork<>(this);
  }

  @SuppressWarnings("unchecked")
  private <N1 extends N, E1 extends E> NetworkBuilder<N1, E1> cast() {
    return (NetworkBuilder<N1, E1>) this;
  }

    putEdge(N1, N1);
    putEdge(N1, N2);
    assertThat(graph.adjacentNodes(N1)).containsExactly(N1, N2);
  }

  @Test
  public void predecessors_selfLoop() {
    assume().that(graph.allowsSelfLoops()).isTrue();

    putEdge(N1, N1);
    assertThat(graph.predecessors(N1)).containsExactly(N1);
    putEdge(N1, N2);
    assertThat(graph.predecessors(N1)).containsExactly(N1, N2);
  }

  @Test

    putEdge(N1, N1);
    assertThat(graph.predecessors(N1)).containsExactly(N1);
    putEdge(N4, N1);
    assertThat(graph.predecessors(N1)).containsExactly(N1, N4);
  }

  @Test
  public void successors_selfLoop() {
    assume().that(graph.allowsSelfLoops()).isTrue();

    putEdge(N1, N1);
    assertThat(graph.successors(N1)).containsExactly(N1);
    putEdge(N1, N2);

    addEdge(N1, N1, E11);
    assertThat(network.successors(N1)).containsExactly(N1);
    addEdge(N2, N1, E12);
    assertThat(network.successors(N1)).containsExactly(N1, N2);
  }

  @Test
  public void degree_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.degree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.degree(N1)).isEqualTo(3);

    assertThat(networkForTest.edgesConnecting(N1, N1)).containsExactly(E11);
    network.addEdge(N1, N2, E12);
    assertThat(networkForTest.edgesConnecting(N1, N2)).containsExactly(E12);
    assertThat(networkForTest.edgesConnecting(N1, N1)).containsExactly(E11);
  }

  @Test
  public void edgesConnecting_parallelEdges() {
    network.addEdge(N1, N2, E12);
    network.addEdge(N1, N2, E12_A);
    network.addEdge(N2, N1, E21);