@Test(expected = IllegalStateException.class)
    @FeatureRequirementSet(FeatureRequirementSet.Package.VERTICES_ONLY)
    public void shouldNotAllowAddEdge() {
        final Vertex v = graph.addVertex();
        final ReferenceVertex rv = ReferenceFactory.detach(v);
        rv.addEdge("test", null);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/structure/util/reference/ReferenceVertexTest.java