ENH: Add a bit more checking to NEXRAD test
ENH: Add a bit more checking to NEXRAD test

At least check that we get the right amount of data.

ShawnMurd/MetPy,ahaberlie/MetPy,Unidata/MetPy,jrleeman/MetPy,dopplershift/MetPy,jrleeman/MetPy,ahaberlie/MetPy,dopplershift/MetPy,Unidata/MetPy