networkAsMutableNetwork = (MutableNetwork<Integer, String>) network;
    }
  }

  @After
  public void validateNetworkState() {
    validateNetwork(network);
  }

  static <N, E> void validateNetwork(Network<N, E> network) {
    assertStronglyEquivalent(network, Graphs.copyOf(network));
    assertStronglyEquivalent(network, ImmutableNetwork.copyOf(network));

    Network<Integer, String> transpose = transpose(directedGraph);
    assertThat(transpose).isEqualTo(expectedTranspose);
    assertThat(transpose(transpose)).isSameInstanceAs(directedGraph);
    AbstractNetworkTest.validateNetwork(transpose);

    assertThat(transpose.edgesConnecting(N1, N2)).isEmpty();
    assertThat(transpose.edgeConnecting(N1, N2).isPresent()).isFalse();
    assertThat(transpose.edgeConnectingOrNull(N1, N2)).isNull();