@Test
public void testAddEdge() {

    graph.addVertex();
    graph.addVertex();
    int e = graph.addEdge(0, 1, null);
    assertEquals(2, graph.getVertexCount());
    assertEquals(0, e);
    assertEquals(1, graph.getEdgeCount());
    assertEquals(0, graph.getEdgeVertex1(e));
    assertEquals(1, graph.getEdgeVertex2(e));
}