At the beginning of this book, we set out the primary tenets of clean code. Among these was reliability. There truly is no greater way to confirm reliability than to expose your code base to continued and multivariate usage. This means having real users sit in front of your software and use it, for real. Only via this type of exposure can we understand whether our code truly fulfills its purpose. However, it is usually unreasonable, and possibly even dangerous, to conduct such real-life tests constantly. If code is changed, it is possible for a piece of functionality that a user relies on to falter or regress. To prevent such cases, and to generally confirm that our expectations are met, we write tests. Without a good suite of tests, we are passively and arrogantly closing our eyes and hoping that nothing goes wrong. 

In this chapter, we'll be covering the following topics:

• What is a test?
• Types of testing
• Test-Driven Development (TDD)