@Override
        public Traversal<Vertex, Map<String, Number>> get_g_V_groupXaX_byXlabelX_byXoutE_weight_sumX_capXaX() {
            return g.V().<String, Double>group("a").by(T.label).by(outE().values("weight").sum()).cap("a");
        }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/GroupTest.java