assertThat(transpose).isEqualTo(expectedTranspose);
    assertThat(transpose(transpose)).isSameInstanceAs(directedGraph);
    AbstractGraphTest.validateGraph(transpose.asGraph());

    assertThat(transpose.edgeValueOrDefault(N1, N2, null)).isNull();
    for (Integer node : directedGraph.nodes()) {
      assertThat(directedGraph.inDegree(node)).isSameInstanceAs(transpose.outDegree(node));