We’ve seen that bad code is bad news: bad for business, bad for users, and bad for developers. Test-driven development (TDD) is a core software engineering practice that helps us keep bad code out of our systems.

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Chapter goals

The goal of this chapter is to learn the specifics of how TDD helps us create well-engineered, correct code, and how it helps us to keep it that way. By the end, we’ll understand the basic principles behind good code and how TDD helps us create it. It’s important for us to understand why TDD works in order to motivate us and so that we have a response to give to colleagues about why we recommend that they use it as well. In this section, we’re going to cover the following main topics:

Getting Started

Building the Case for TDD

Using TDD to Create Good Code

Dispelling Common Myths about TDD

Building an Application Using TDD

Writing Our First Test

Following the Rhythms of TDD

Driving Design—TDD and SOLID

Test Doubles—Stubs and Mocks

Hexagonal Architecture—Decoupling External Systems

FIRST Tests and the Test Pyramid

Exploring TDD with Quality Assurance

Test First, Test Later, Test Never

Driving the Domain Layer

Driving the Database Layer

Driving the Web Layer

Wrap Up

Appendix

Introduction: Using TDD to Create Good Code

Chapter goals