@Test
    @LoadGraphWith(MODERN)
    public void g_V_group_byXageX() {
        final Traversal<Vertex, Map<Integer, Collection<Vertex>>> traversal = get_g_V_group_byXageX();
        printTraversalForm(traversal);

        final Map<Integer, Collection<Vertex>> map = traversal.next();
        assertEquals(4, map.size());
        map.forEach((key, values) -> {
            if (null == key)
                assertEquals(2, values.size());
            else
                assertEquals(1, values.size());
        });
        assertFalse(traversal.hasNext());

        checkSideEffects(traversal.asAdmin().getSideEffects());
    }
@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