Add unittest for Variable.set_creator
Add unittest for Variable.set_creator

ysekky/chainer,chainer/chainer,chainer/chainer,woodshop/chainer,jnishi/chainer,ronekko/chainer,truongdq/chainer,truongdq/chainer,minhpqn/chainer,hidenori-t/chainer,okuta/chainer,elviswf/chainer,tscohen/chainer,t-abe/chainer,tkerola/chainer,benob/chainer,laysakura/chainer,sinhrks/chainer,ikasumi/chainer,hvy/chainer,kikusu/chainer,cemoody/chainer,chainer/chainer,AlpacaDB/chainer,okuta/chainer,muupan/chainer,sinhrks/chainer,niboshi/chainer,Kaisuke5/chainer,umitanuki/chainer,cupy/cupy,cupy/cupy,hvy/chainer,yanweifu/chainer,keisuke-umezawa/chainer,AlpacaDB/chainer,t-abe/chainer,kuwa32/chainer,hvy/chainer,keisuke-umezawa/chainer,niboshi/chainer,kikusu/chainer,keisuke-umezawa/chainer,rezoo/chainer,niboshi/chainer,hvy/chainer,benob/chainer,1986ks/chainer,delta2323/chainer,wavelets/chainer,okuta/chainer,ytoyama/yans_chainer_hackathon,sou81821/chainer,kiyukuta/chainer,chainer/chainer,ktnyt/chainer,jnishi/chainer,ktnyt/chainer,wkentaro/chainer,ktnyt/chainer,pfnet/chainer,masia02/chainer,wkentaro/chainer,cupy/cupy,ktnyt/chainer,woodshop/complex-chainer,aonotas/chainer,tigerneil/chainer,wkentaro/chainer,okuta/chainer,cupy/cupy,niboshi/chainer,anaruse/chainer,jnishi/chainer,keisuke-umezawa/chainer,jnishi/chainer,muupan/chainer,wkentaro/chainer,kashif/chainer