() -> networkAsMutableNetwork.addEdge(N2, N1, EDGE_NOT_IN_GRAPH));
    assertThat(e).hasMessageThat().contains(ERROR_PARALLEL_EDGE);
  }

  @Test
  public void addEdge_parallelEdge_allowsParallelEdges() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsParallelEdges()).isTrue();

    assertThat(networkAsMutableNetwork.addEdge(N1, N2, E12)).isTrue();