@Test
public void testRemoveEdge() {

    graph.addVertex();
    graph.addVertex();
    graph.addVertex();
    int e = graph.addEdge(0, 1, null);
    graph.removeEdge(e);
    assertEquals(0, graph.getEdgeCount());
    e = graph.addEdge(0, 1, null);
    assertEquals(0, e);
    int e2 = graph.addEdge(1, 2, null);
    graph.removeEdge(e);
    assertEquals(1, graph.getEdgeCount());
    e = graph.addEdge(0, 1, null);
    assertEquals(0, e);
    graph.removeEdge(e);
    graph.removeEdge(e2);
    assertEquals(0, graph.getEdgeCount());
}