Unit testing is an essential instrument in the toolbox of any serious software developer. However, it can sometimes be quite difficult to write a good unit test for a particular piece of code. Having difficulty testing their own or someone else’s code, developers often think that their struggles are caused by a lack of some fundamental testing knowledge or secret unit testing techniques.
In this article, I would like to show that unit tests are quite easy; the real problems that complicate unit testing, and introduce expensive complexity, are a result of poorly-designed, untestable code. We will discuss what makes code hard to test, which anti-patterns and bad practices we should avoid to improve testability, and what other benefits we can achieve by writing testable code. We will see that writing testable code is not just about making testing less troublesome, but about making the code itself more robust, and easier to maintain.