Add test about types of return value of interval method
Add test about types of return value of interval method

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