FIRST Tests and the Test Pyramid

So far in this book, we’ve seen the value of writing unit tests that run quickly and give repeatable results. Called FIRST tests, these provide rapid feedback on our design. They are the gold standard of unit tests. We’ve also seen how the hexagonal architecture helps us design our code in a way that gets the maximum amount covered by FIRST unit tests. But we’ve also limited ourselves to testing only our domain model – the core of our application logic. We simply have no tests covering how our domain model behaves once it connects to the outside world.

In this chapter, we will cover all the other kinds of tests that we need. We will introduce the test pyramid, which is a way of thinking about the different kinds of tests needed, and how many of each we should have. We’ll discuss what each kind of test covers and useful techniques and tools to help. We’ll also bring the whole system together by introducing...