'In an empty L{base.PositionError} with invariant testing, all
dilutions of positions are L{None}.'

def test_allUnsetWithInvariant(self):

    positionError = base.PositionError(testInvariant=True)
    self.assertIsNone(positionError.pdop)
    self.assertIsNone(positionError.hdop)
    self.assertIsNone(positionError.vdop)
