skip sparse tests if sparse library not present (#2424)
skip sparse tests if sparse library not present (#2424)


mrocklin/dask,jakirkham/dask,jakirkham/dask,jcrist/dask,ContinuumIO/dask,mrocklin/dask,ContinuumIO/dask,jcrist/dask,blaze/dask,blaze/dask,dask/dask,dask/dask