expectedClosure.putEdge(N1, N3);
    expectedClosure.putEdge(N2, N2);
    expectedClosure.putEdge(N2, N3);
    expectedClosure.putEdge(N3, N3);
    expectedClosure.putEdge(N4, N4);

    checkTransitiveClosure(directedGraph, expectedClosure);
  }

  @Test
  public void transitiveClosure_undirectedGraph() {
    MutableGraph<Integer> undirectedGraph =
        GraphBuilder.undirected().allowsSelfLoops(false).build();