Test-driven class design

It's not enough to distinguish between different types of tests and learn a particular testing framework (or several). When you start testing your actual code, you will soon notice that not all classes can be tested easily. Sometimes, you may feel the need to access private attributes or methods. Resist this urge if you want to maintain the principles of good architecture! Instead, consider either testing the business requirements that are available through the type's public API or refactoring the type so that there's another unit of code you can test.