advise about secure tests in python

Im pretty begginer with python and I'm having trouble to understand what is the deffrence between unit testing and secure testing. what am I trying to do when performing secure testing?

My goal is to preform some secure testing on FTP server/client but I really dont know where to begin with out wasting time.

Please tell me which from this list I came across on google are good start to get some understanding about secure testing on FTP server/client:

mock , python unittest, the book- Python Penetration Testing Essentials (180 pages).