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

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