    assert g.vertices == {0:(0.2,0.5), 5:(1,2)}
    assert g.edges == [(0,5)]

    b1 = network.PlanarGraphBuilder(g)
    assert b1.add_vertex(5,6) == 6
    b1.add_edge(5,6)
    g1 = b1.build()
    assert g1.vertices == {0:(0.2,0.5), 5:(1,2), 6:(5,6)}
    assert g1.edges == [(0,5), (5,6)]