Add heartbeat test.
Add heartbeat test.

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