Add unittests for ComputationalGraph.nodes
Add unittests for ComputationalGraph.nodes

yanweifu/chainer,laysakura/chainer,bayerj/chainer,kikusu/chainer,cupy/cupy,delta2323/chainer,jfsantos/chainer,pfnet/chainer,ktnyt/chainer,elviswf/chainer,jnishi/chainer,niboshi/chainer,kashif/chainer,chainer/chainer,okuta/chainer,aonotas/chainer,wavelets/chainer,sinhrks/chainer,Kaisuke5/chainer,niboshi/chainer,cupy/cupy,ronekko/chainer,truongdq/chainer,hvy/chainer,niboshi/chainer,jnishi/chainer,benob/chainer,muupan/chainer,wkentaro/chainer,muupan/chainer,AlpacaDB/chainer,tigerneil/chainer,wkentaro/chainer,hvy/chainer,anaruse/chainer,ikasumi/chainer,niboshi/chainer,sinhrks/chainer,ktnyt/chainer,woodshop/chainer,tscohen/chainer,sou81821/chainer,chainer/chainer,wkentaro/chainer,ytoyama/yans_chainer_hackathon,chainer/chainer,AlpacaDB/chainer,keisuke-umezawa/chainer,masia02/chainer,t-abe/chainer,umitanuki/chainer,wkentaro/chainer,ktnyt/chainer,tkerola/chainer,cupy/cupy,ktnyt/chainer,tereka114/chainer,keisuke-umezawa/chainer,t-abe/chainer,okuta/chainer,hvy/chainer,keisuke-umezawa/chainer,kuwa32/chainer,cupy/cupy,hvy/chainer,truongdq/chainer,1986ks/chainer,rezoo/chainer,chainer/chainer,okuta/chainer,woodshop/complex-chainer,okuta/chainer,kiyukuta/chainer,keisuke-umezawa/chainer,benob/chainer,hidenori-t/chainer,kikusu/chainer,cemoody/chainer,minhpqn/chainer,jnishi/chainer,jnishi/chainer,ysekky/chainer