@Test
  public void hasCycle_emptyGraph() {
    assertThat(hasCycle(directedGraph)).isFalse();
    assertThat(hasCycle(undirectedGraph)).isFalse();
  }

  @Test
  public void hasCycle_isolatedNodes() {
    for (MutableGraph<Integer> graph : graphsToTest) {
      graph.addNode(1);
      graph.addNode(2);
    }
    assertThat(hasCycle(directedGraph)).isFalse();
    assertThat(hasCycle(undirectedGraph)).isFalse();
  }

  private static final int NUM_NODES = 100;
  private static final int NUM_EDGES = 1000;
  private static final int NODE_POOL_SIZE = 1000; // must be >> NUM_NODES

  @Test
  public void directedGraph() {
    testGraphMutation(GraphBuilder.directed());
  }

  @Test
  public void undirectedGraph() {
    testGraphMutation(GraphBuilder.undirected());
  }

  private static final int NUM_NODES = 100;
  private static final int NUM_EDGES = 1000;
  private static final int NODE_POOL_SIZE = 1000; // must be >> NUM_NODES

  @Test
  public void directedGraph() {
    testGraphMutation(GraphBuilder.directed());
  }

  @Test
  public void undirectedGraph() {
    testGraphMutation(GraphBuilder.undirected());
  }