How to make the bot reply to any message?

Question

Python

That is, when if message.text == is empty. The code does not work what needs to be put in brackets so that any message is read.

@bot.message_handler(commands=['test'])
def test(message):
    bot.send_message(message.chat.id, 'Напишите что-то')
    if message.text == '':
        bot.send_message(message.chat.id, 'Спасибо')