Adding Tests First

In this lesson, we’ll review the trade-offs of adding a test first before writing the production code to make it pass. Previous chapters have followed a test-first approach to writing code. We write a test before writing production code to make that test pass. This is a recommended approach, but it’s important to understand some of the difficulties associated with it as well as consider its benefits.

Test-first is a design tool

The most important benefit of writing tests first is that a test acts as a design aid. As we decide what to write in our test, we’re designing the interface to our code. Each of the test stages helps us consider an aspect of software design, as shown by the following illustration: