@Test
  public void testFlagFeedbackEdgesOnSimpleLoop() {
    DirectedGraph<String, StringEdge> dcg = DirectedGraph.createStringDirectedGraph();
    dcg.addEdge("A", "B", 3).addEdge("B", "A", 1);
    CycleDetector<String> cycleDetector = new CycleDetector<String>(dcg);
    cycleDetector.detectCycles();

    MinimumFeedbackEdgeSetSolver solver =
        new MinimumFeedbackEdgeSetSolver(cycleDetector.getCycles());
    Set<Edge> feedbackEdges = solver.getEdges();
    assertTrue(feedbackEdges.contains(dcg.getEdge("B", "A")));
  }
  @Test
  public void testGetFeedbackEdgesOnComplexGraph() {
    DirectedGraph<String, StringEdge> dcg = DirectedGraph.createStringDirectedGraph();
    dcg.addEdge("A", "B", 7).addEdge("B", "C", 3).addEdge("C", "D", 1).addEdge("D", "A", 3);
    dcg.addEdge("B", "A", 12);
    CycleDetector<String> cycleDetector = new CycleDetector<String>(dcg);
    cycleDetector.detectCycles();

    MinimumFeedbackEdgeSetSolver solver =
        new MinimumFeedbackEdgeSetSolver(cycleDetector.getCycles());
    Set<Edge> feedbackEdges = solver.getEdges();
    assertThat(feedbackEdges.size(), is(1));

    assertTrue(feedbackEdges.contains(dcg.getEdge("A", "B")));
  }
  @Test
  public void testApproximateMinimumFeedbackEdges() {
    DirectedGraph<String, StringEdge> dcg = DirectedGraph.createStringDirectedGraph();
    dcg.addEdge("A", "B", 5).addEdge("B", "C", 9).addEdge("C", "A", 1);
    dcg.addEdge("D", "B", 5).addEdge("C", "D", 7);
    dcg.addEdge("F", "B", 5).addEdge("C", "F", 4);
    CycleDetector<String> cycleDetector = new CycleDetector<String>(dcg);
    cycleDetector.detectCycles();

    MinimumFeedbackEdgeSetSolver minimumSolver =
        new MinimumFeedbackEdgeSetSolver(cycleDetector.getCycles());
    assertThat(minimumSolver.getEdges().size(), is(1));
    assertTrue(minimumSolver.getEdges().contains(dcg.getEdge("B", "C")));

    MinimumFeedbackEdgeSetSolver approximateSolver =
        new MinimumFeedbackEdgeSetSolver(cycleDetector.getCycles(), 2);
    assertThat(approximateSolver.getEdges().size(), is(2));
    assertTrue(approximateSolver.getEdges().contains(dcg.getEdge("B", "C")));
    assertTrue(approximateSolver.getEdges().contains(dcg.getEdge("C", "A")));
  }
  @Test
  public void testFlagFeedbackEdgesOnUnrelatedCycles() {
    DirectedGraph<String, StringEdge> dcg = DirectedGraph.createStringDirectedGraph();
    dcg.addEdge("A", "B", 7).addEdge("B", "C", 3).addEdge("C", "A", 2);
    dcg.addEdge("D", "E", 3).addEdge("E", "D", 5);
    dcg.addEdge("F", "G", 1).addEdge("G", "H", 4).addEdge("H", "F", 7);

    CycleDetector<String> cycleDetector = new CycleDetector<String>(dcg);
    cycleDetector.detectCycles();

    MinimumFeedbackEdgeSetSolver solver =
        new MinimumFeedbackEdgeSetSolver(cycleDetector.getCycles());
    Set<Edge> feedbackEdges = solver.getEdges();

    assertThat(feedbackEdges.size(), is(3));

    assertTrue(feedbackEdges.contains(dcg.getEdge("C", "A")));
    assertTrue(feedbackEdges.contains(dcg.getEdge("D", "E")));
    assertTrue(feedbackEdges.contains(dcg.getEdge("F", "G")));
  }