Let me talk about the interested mentor I met. They wrote more e-mail replies. First, they welcomed me, and then said that they thought I was suitable for their research group, or asked me to post my articles and my experimental things or ask me to meet directly. Then the teacher will directly say that you can test me as long as you pass the initial test.
When you decide, you should always contact the teacher. If you have nothing to do, just ask if the professional class can draw a range for you or something. When you go to see them, you can bring a small gift, which is not expensive 100.