'Test MHZClient when ppm is too high.'

@patch('pmsensor.co2sensor.read_mh_z19_with_temperature', return_value=(5001, 24))
def test_client_update_ppm_overflow(self, mock_function):

    from pmsensor import co2sensor
    client = mhz19.MHZClient(co2sensor, 'test.serial')
    client.update()
    self.assertIsNone(client.data.get('co2'))
