Refactoring for readability, Separating tests

[RichardPflaum]

Hi, I found your project when I was about to write the same thing. Thank you for sharing! I cleaned it up a bit, to make the decorator implementation more readable and created several test cases from your existing one. The separated tests improve insight, which cases are actually working, which was already helpful refactoring. Maybe this will help to fix the open issues. :) Best, Richard