def test_positionAndVerticalSet(self):
        """
        The HDOP is correctly determined from PDOP and VDOP.
        """
        pdop, vdop = 2.0, 1.0
        hdop = (pdop**2 - vdop**2)**.5
        pe = base.PositionError(pdop=pdop, vdop=vdop)
        self._testDOP(pe, pdop, hdop, vdop)

        The HDOP is correctly determined from PDOP and VDOP.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/positioning/test/test_base.py