Introduction

• Understanding the importance of effective, systematic testing
• Recognizing why testing software is difficult and why bug-free systems do not exist
• Introducing the testing pyramid

The developer community no longer needs to argue about the importance of software testing. Every software developer understands that software failures may cause severe damage to businesses, people, or even society as a whole. And although software developers once were primarily responsible for building software systems, today they are also responsible for the quality of the software systems they produce.

Our community has produced several world-class tools to help developers test, including JUnit, AssertJ, Selenium, and jqwik. We have learned to use the process of writing tests to reflect on what programs need to do and get feedback about the code design (or class design, if you are using an object-oriented language). We have also learned that writing test code is challenging, and paying attention to test code quality is fundamental for the graceful evolution of the test suite. And finally, we know what the common bugs are and how to look for them.

But while developers have become very good at using testing tools, they rarely apply systematic testing techniques to explore and find bugs. Many practitioners argue that tests are a feedback tool and should be used mostly to help you develop. How to listen to your test code), tests can also help you find bugs. After all, that is what software testing is all about: finding bugs!

Most developers do not enjoy writing tests. I have heard many reasons: writing production code is more fun and challenging, software testing is too time-consuming, we are paid to write production code, and so on. Developers also overestimate how much time they spend on testing, as Beller and colleagues found in a nice empirical study with hundreds of developers in 2019. It is your responsibility to ensure the quality of what you produce; (2) that tests are the only tools to help you with that responsibility; and (3) that if you follow a collection of techniques, you can test your code in an effective and systematic way.

Note the words I used: effective and systematic. Soon you will understand what I mean. But first, let me convince you of the necessity of tests.