BROOKLYN — Jarrett Allen’s first test of the season came less than six minutes into opening night as the Nets faced the Pistons at Little Caesars Arena in Detroit. Blake Griffin bullied his way past Brooklyn sharpshooter Joe Harris on the right elbow with 6:30 remaining in the first quarter, then elevated toward the rim to attempt a thunderous one-hand slam. But Griffin couldn’t complete another patented poster. Instead, Allen met Griffin at the peak of his jump, spiking the ball back onto the hardwood. A wry smile emerged on Allen’s face as the Nets’ bench leapt in celebration.