'Test filter life sensor with no value.'

def test_dyson_filter_life_sensor(self):

    sensor = dyson.DysonFilterLifeSensor(self.hass, _get_device_without_state())
    sensor.entity_id = 'sensor.dyson_1'
    self.assertFalse(sensor.should_poll)
    self.assertIsNone(sensor.state)
    self.assertEqual(sensor.unit_of_measurement, 'hours')
    self.assertEqual(sensor.name, 'Device_name    filter    life')
    self.assertEqual(sensor.entity_id, 'sensor.dyson_1')
    sensor.on_message('message')
