In earlier lessons, we explored the fundamentals of Test-Driven Development (TDD), including the Red-Green-Refactor cycle and setting up a testing environment. Now, we’ll focus on managing dependencies, an essential practice for isolating units of code and ensuring tests are reliable and independent.

We’ll use traits in Scala to manage dependencies. Traits serve as contracts for abstractions, allowing you to decouple components and make them easier to test. This lesson will demonstrate how to apply the Red-Green-Refactor cycle to dependency management using Scala and ScalaTest.

Dependencies are external components that your code interacts with. Managing them effectively ensures that your tests are independent of these external factors. This can be achieved using traits, which allow us to define abstractions and swap implementations easily.

For example, a logger that a class uses can be abstracted as a trait. This lets us replace the actual logger with a mock during testing, focusing solely on the logic under test.

The Logger trait defines a single log method. This abstraction allows different logging implementations, such as a real logger in production or a mock logger in tests.

Let’s create a UserManager class that depends on the Logger trait. To keep it decoupled, we’ll inject the logger dependency through the constructor.