Many think that the big step from "coding" to "software engineering" is made by having elegant architectures, well-defined execution plans, and software that moves big companies' processes. This mostly comes from our vision of the classic industrial product development world, where planning mostly mattered more than execution, because the execution was moved forward by an assembly line and software was an expensive internal utility that only big companies could afford

As software development science moved forward and matured, it became clear that classic industrial best practices weren't always a great fit for it. The reason being that every software product was very different, due to the technologies involved, the speed at which those technologies evolve, and in the end the fact that different software had to do totally different things. Thus the idea developed that software development was more similar to craftsmanship than to industry.

If you embrace that it's very hard, and not very effective, to try to eliminate uncertainty and issues with tons of preparation work due to the very nature of software itself, it becomes evident that the most important part of software development is detecting defects and ensuring it achieves the expected goals. Those two things are usually mostly done by having tests and a fitness function that can verify the software does what we really mean it to – founding pieces of the whole Software Quality Control discipline, which is what this chapter will introduce and, in practice, what this book is all about.

In this chapter, we will go through testing software products and the best practices in quality control. We will also introduce automatic tests and how they are superseding manual testing. We will take a look at what Test-Driven Development (TDD) is and how to apply it in Python, giving some guidance on how to distinguish between the various categories of tests, how to implement them, and how to get the right balance between test efficacy and test cost.

In this chapter, we will cover the following:

• Introducing software testing and quality control
• Introducing automatic tests and test suites
• Introducing test-driven development and unit tests
• Understanding integration and functional tests
• Understanding the testing pyramid and trophy