Refactor and add tests for plugins.py

Improvement to the tests currently being run on ``plugins.py``

related #644 
I wrote this code in 2011. I'm positive I wouldn't have put it there if there wasn't a good reason to, I just wish I wrote down in the comment why it put it there (this is exactly why us mentors keep nitpicking about properly commenting code, it might be obvious to you when you wrote it but when you have to look at it again a few years later you're gonna forget).

What I'm doing here is overriding the default __call__() function to make it do nothing probably because I did not like the behaviour of it. Anyway you don't need to look into it but my point is you shouldn't remove code if you don't know why it was put there (or what it's doing) in the first place as it could have implications you didn't think of.