Improve test for to_cpu
Improve test for to_cpu

hvy/chainer,cupy/cupy,rezoo/chainer,jnishi/chainer,chainer/chainer,AlpacaDB/chainer,hvy/chainer,ysekky/chainer,aonotas/chainer,cupy/cupy,wkentaro/chainer,okuta/chainer,ktnyt/chainer,chainer/chainer,cupy/cupy,keisuke-umezawa/chainer,hvy/chainer,anaruse/chainer,ktnyt/chainer,ktnyt/chainer,keisuke-umezawa/chainer,kiyukuta/chainer,chainer/chainer,keisuke-umezawa/chainer,cupy/cupy,ronekko/chainer,niboshi/chainer,wkentaro/chainer,pfnet/chainer,okuta/chainer,chainer/chainer,jnishi/chainer,okuta/chainer,wkentaro/chainer,kikusu/chainer,niboshi/chainer,jnishi/chainer,hvy/chainer,keisuke-umezawa/chainer,benob/chainer,tkerola/chainer,ktnyt/chainer,benob/chainer,jnishi/chainer,niboshi/chainer,kikusu/chainer,niboshi/chainer,kashif/chainer,okuta/chainer,AlpacaDB/chainer,wkentaro/chainer,delta2323/chainer