This is an example project with code that exhibits common issues that make it hard to write tests.
The exercise is to take the current implementation of the Yucky class, refactor it into testable code, and add those tests.
My recommended approach is to look at the code, write down the issues that you have found, and take a try at refactoring. Then, go and read the "You suck at TDD series", come back, and see if you have any new thoughts.