The ideas explored in this chapter are fundamental pillars in the global context of the book, because of their importance towards our ultimate goal: to write better and more maintainable software.

Unit tests (and any form of automatic tests, for that matter) are critical to software maintainability, and therefore are something that cannot be missing from any quality project. It is for that reason that this chapter is dedicated exclusively to aspects of automated testing as a key strategy, to safely modify the code, and iterate over it, in incrementally better versions.

After this chapter, we will have gained more insight into the following:

• Why automated tests are critical for projects that run under an agile software development methodology
• How unit tests work as a heuristic of the quality of the code
• What frameworks and tools are available to develop automated tests and set up quality gates
• Taking advantage of unit tests to understand the domain problem better and document code
• Concepts related to unit testing, such as test-driven development