directedGraph.putEdge(N2, N1);
    // View should be updated.
    assertThat(transpose.successors(N1)).contains(N2);
    AbstractGraphTest.validateGraph(transpose);
  }

  @Test
  public void transpose_undirectedValueGraph() {
    MutableValueGraph<Integer, String> undirectedGraph = ValueGraphBuilder.undirected().build();
    undirectedGraph.putEdgeValue(N1, N2, E12);