addEdge(N1, N1, E11);
    addEdge(N1, N2, E12);
    assertThat(network.adjacentEdges(E11)).containsExactly(E12);
  }

  @Test
  public void edgesConnecting_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11);
    addEdge(N1, N2, E12);

        Graph graph3 = new Graph();
        addEdge(graph3, "a", "b");
        addEdge(graph3, "b", "c");
        addEdge(graph3, "b", "d");
        addEdge(graph3, "a", "d");

        Graph graph4 = new Graph();
        addEdge(graph4, "a", "b");
        addEdge(graph4, "b", "c");
        addEdge(graph4, "b", "d");
        addEdge(graph4, "a", "d");

        // v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

        // v1-->v3
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.2", true, null, null, 4, 2));

        // v3-->v4

  }

  @Test
  public void edgesConnecting_directed() {
    MutableNetwork<String, String> mutableNetwork =
        NetworkBuilder.directed().allowsSelfLoops(true).build();
    mutableNetwork.addEdge("A", "A", "AA");
    mutableNetwork.addEdge("A", "B", "AB");
    Network<String, String> network = ImmutableNetwork.copyOf(mutableNetwork);

    assertThat(network.edgesConnecting("A", "A")).containsExactly("AA");

                if (vertex != null) {
                    addEdge(projectVertex, vertex, project, projectMap, force, safe);
                }
            } else {
                for (Vertex vertex : vertices.values()) {
                    addEdge(projectVertex, vertex, project, projectMap, force, safe);
                }
            }
        }
    }

    private void addEdge(
            Vertex fromVertex,

   *         .allowsParallelEdges(true)
   *         .<City, Train>immutable()
   *         .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
   *         .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))
   *         .addEdge(LONDON, PARIS, Eurostar.trainNumber("3333"))
   *         .addEdge(LONDON, BRUSSELS, Eurostar.trainNumber("4444"))
   *         .addNode(REYKJAVIK)
   *         .build();
   * }</pre>

   *         .allowsParallelEdges(true)
   *         .<City, Train>immutable()
   *         .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
   *         .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))
   *         .addEdge(LONDON, PARIS, Eurostar.trainNumber("3333"))
   *         .addEdge(LONDON, BRUSSELS, Eurostar.trainNumber("4444"))
   *         .addNode(REYKJAVIK)
   *         .build();
   * }</pre>

 * flightNetwork.addEdge("LAX", "ATL", 3025);
 * flightNetwork.addEdge("LAX", "ATL", 1598);
 * flightNetwork.addEdge("ATL", "LAX", 2450);
 *
 * // Building a immutable network
 * ImmutableNetwork<String, Integer> immutableNetwork =
 *     NetworkBuilder.directed()
 *         .allowsParallelEdges(true)
 *         .<String, Integer>immutable()
 *         .addEdge("LAX", "ATL", 3025)

public class GraphTest {

    @Test
    void testCycle() throws Graph.CycleDetectedException {
        Graph graph = new Graph();
        graph.addEdge("a1", "a2");
        assertThrows(Graph.CycleDetectedException.class, () -> graph.addEdge("a2", "a1"));
    }

    @Test
    public void testPerf() throws IOException {
        List<String[]> data = new ArrayList<>();
        String k = null;

        // v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

        // v1-->v3
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.2", true, null, null, 4, 2));

        // v3-->v4