improve cull test
improve cull test

ssanderson/dask,clarkfitzg/dask,chrisbarber/dask,jayhetee/dask,mikegraham/dask,vikhyat/dask,jakirkham/dask,gameduell/dask,dask/dask,pombredanne/dask,PhE/dask,ContinuumIO/dask,ssanderson/dask,jcrist/dask,wiso/dask,pombredanne/dask,jayhetee/dask,clarkfitzg/dask,vikhyat/dask,mrocklin/dask,ContinuumIO/dask,jakirkham/dask,mraspaud/dask,cowlicks/dask,blaze/dask,dask/dask,PhE/dask,mraspaud/dask,wiso/dask,blaze/dask,jcrist/dask,cpcloud/dask,mrocklin/dask