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

    assertThat(transpose(undirectedGraph)).isSameInstanceAs(undirectedGraph);
  }

  @Test
  public void transpose_directedValueGraph() {
    MutableValueGraph<Integer, String> directedGraph =

 * ValueGraphBuilder} class:
 *
 * <pre>{@code
 * MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build();
 * }</pre>
 *
 * <p>{@link ValueGraphBuilder#build()} returns an instance of {@link MutableValueGraph}, which is a
 * subtype of {@code ValueGraph} that provides methods for adding and removing nodes and edges. If