In previous lessons, we've explored the fundamentals of Test Driven Development (TDD) — the Red-Green-Refactor cycle — and how to set up a testing environment using Go and the Testify library. Now, we shift our focus to a key aspect of TDD: managing dependencies. Managing dependencies ensures that each unit of your application can be tested in isolation, which is crucial in TDD for maintaining code reliability and robustness.

In this lesson, we will examine how to use interfaces for abstraction in Go, allowing us to effectively manage dependencies. Using simple examples, we will demonstrate applying the Red-Green-Refactor cycle in this context. Let’s dive in.

Dependencies in software development refer to the components or systems on which a piece of code relies to function properly. In the context of testing, dependencies can complicate unit tests because they might introduce external factors that affect the test outcomes. To ensure tests are isolated and independent, we use abstractions.

An interface in Go acts as a type that defines method signatures without implementations. By programming against interfaces, you can easily swap out implementations, making code more modular and test-friendly.

For example, consider a logger that a component uses to record actions. By abstracting the logger using an interface, you decouple the component from a specific logging implementation. This abstraction allows you to replace the actual logger with a mock or fake when testing, thus focusing on testing the component, not its dependencies.

We'll create a simple logger interface called Logger to demonstrate dependency management. This interface will define a method Log, which our will use: