Inside-Out vs. Outside-In Testing in TDD
Explore the contrasting paths of TDD: inside-out for robustness, outside-in for user value, and find harmony through hexagonal architecture.
In this lesson, we’re going to review our choice of starting point for our TDD activities. The first place to look at is inside our software system, starting with details.
An inside-out approach with TDD
When starting to build software, we obviously need some place to start from.
One place to start is with some of the details. Software is made up of small interconnecting components, each of which performs a portion of the whole task. Some components come from library code. Many components are custom-made to provide the functionality our application needs.
One place to start building, then, is on the inside of this software system. Starting with an overall user story, we can imagine a small component that is likely to be of use to us. We can begin our TDD efforts around this component and see where that leads us. This is a bottom-up approach to the design, composing the whole from smaller parts.
The inside-out approach for Wordz
If we consider a simplified version of our Wordz application structure, we can illustrate the inside-out approach as follows:
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