After you spending some time coding and developing, sooner or later you will encounter something called TDD (Test-Driven Development) .
You will hear and read things like
If you want to be a professional developer you need to test your applications
Naturally, you have the drive to be a kick-ass developer and you want to see the fuss is all about. But after researching you will have the feeling that it is all a bit confusing.
The funny thing is that we are all testing already but we are doing it manually through the browser. Now we just need to convert that to code with a tool like codeception.
Find out about the basics of testing:
Try it out. The sooner you start with TDD the sooner you will be getting a much better and more professional developer.