How to use pytest correctly

I'm building my first python package. I noticed an automatic test of the code made directly into GitHub by pytest I surfed for good and clear explanations but I can't figure out myself Is there any way you can help me?

The dir structure:

-> deezepy:
       |
       -> __init__.py
       -> client.py
       -> types.py

-> tests/
       currently empty

what should I put in my test directory? the two files:

client.py -> https://hastebin.com/yoyemirula.py

types.py -> https://hastebin.com/amafegilic.rb

I'm very glad about anybody that can help me using these tools for the first time, thanks!