* subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you
 * do not need to mutate a network (e.g. if you write a method than runs a read-only algorithm on
 * the network), you should use the non-mutating {@link Network} interface, or an {@link
 * ImmutableNetwork}.
 *
 * <p>You can create an immutable copy of an existing {@code Network} using {@link
 * ImmutableNetwork#copyOf(Network)}:

    setDistinctValues(MutableNetwork.class, mutableNetworkA, mutableNetworkB);
    setDistinctValues(NetworkBuilder.class, NETWORK_BUILDER_A, NETWORK_BUILDER_B);
    setDistinctValues(Network.class, IMMUTABLE_NETWORK_A, IMMUTABLE_NETWORK_B);
    setDefault(EndpointPair.class, EndpointPair.ordered("A", "B"));
  }

  @Override
  public void testNulls() throws Exception {
    try {

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

  private static class NetworkForTest<N, E> extends AbstractNetwork<N, E> {
    private final Network<N, E> network;

    NetworkForTest(Network<N, E> network) {
      this.network = network;
    }

      MutableNetwork<Integer, Object> network =
          networkBuilder.allowsParallelEdges(true).allowsSelfLoops(true).build();

      assertThat(network.nodes()).isEmpty();
      assertThat(network.edges()).isEmpty();
      AbstractNetworkTest.validateNetwork(network);

      while (network.nodes().size() < NUM_NODES) {
        network.addNode(gen.nextInt(NODE_POOL_SIZE));
      }

    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.incidentEdges(N1)).containsExactly(E11);
  }

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

    addEdge(N1, N1, E11);
    assertThat(network.incidentNodes(E11).source()).isEqualTo(N1);
    assertThat(network.incidentNodes(E11).target()).isEqualTo(N1);
  }

      MutableNetwork<Integer, Object> network =
          networkBuilder.allowsParallelEdges(true).allowsSelfLoops(true).build();

      assertThat(network.nodes()).isEmpty();
      assertThat(network.edges()).isEmpty();
      AbstractNetworkTest.validateNetwork(network);

      while (network.nodes().size() < NUM_NODES) {
        network.addNode(gen.nextInt(NODE_POOL_SIZE));
      }

    setDistinctValues(MutableNetwork.class, mutableNetworkA, mutableNetworkB);
    setDistinctValues(NetworkBuilder.class, NETWORK_BUILDER_A, NETWORK_BUILDER_B);
    setDistinctValues(Network.class, IMMUTABLE_NETWORK_A, IMMUTABLE_NETWORK_B);
    setDefault(EndpointPair.class, EndpointPair.ordered("A", "B"));
  }

  @Override
  public void testNulls() throws Exception {
    try {

            NetworkBuilder.directed().<Integer, String>build(),
            NetworkBuilder.undirected().<Integer, String>build());
    for (MutableNetwork<Integer, String> network : testNetworks) {
      network.addEdge(1, 2, "1-2");
      EndpointPair<Integer> endpointPair = network.incidentNodes("1-2");
      assertThrows(IllegalArgumentException.class, () -> endpointPair.adjacentNode(3));
    }
  }

  @Test
  public void testEquals() {

            NetworkBuilder.directed().<Integer, String>build(),
            NetworkBuilder.undirected().<Integer, String>build());
    for (MutableNetwork<Integer, String> network : testNetworks) {
      network.addEdge(1, 2, "1-2");
      EndpointPair<Integer> endpointPair = network.incidentNodes("1-2");
      assertThrows(IllegalArgumentException.class, () -> endpointPair.adjacentNode(3));
    }
  }

  @Test
  public void testEquals() {

        assertThat(network.incidentEdges(node).size() + selfLoopCount)
            .isEqualTo(network.inDegree(node) + network.outDegree(node));
        assertThat(network.inEdges(node)).hasSize(network.inDegree(node));
        assertThat(network.outEdges(node)).hasSize(network.outDegree(node));
      } else {
        assertThat(network.predecessors(node)).isEqualTo(network.adjacentNodes(node));