Add test for pressure at height above pressure helper
Add test for pressure at height above pressure helper

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