'Return if select fails to return a socket.'

@patch('socket.socket.connect')
@patch('socket.socket.send')
@patch('select.select', return_value=(False, False, False))
def test_update_returns_if_select_fails(self, *args):

    with patch('homeassistant.components.sensor.tcp.TcpSensor.update'):
        sensor = tcp.TcpSensor(self.hass, TEST_CONFIG['sensor'])
    assert (sensor.update() is None)
