In this lesson, we'll deepen our understanding of the Test-Driven Development (TDD) mindset using Scala 3 and ScalaTest by focusing on the Red-Green-Refactor cycle. We'll work through a practical example centered on a calculateTotal function, guiding you through thinking with tests, prioritizing test writing, and leveraging TDD to enhance code clarity, reliability, and maintainability.

Using Scala and ScalaTest, we'll follow these steps:

• Begin with the Red phase by identifying and writing failing tests for the calculateTotal function, which will compute the total price of items in a shopping cart.
• Move to the Green phase to implement the minimal code required to pass each test, ensuring that the calculateTotal function behaves as expected.
• Enter the Refactor phase to improve the code structure and readability of calculateTotal, employing Scala’s functional programming features for aggregation while keeping tests green.
• Utilize ScalaTest as the testing framework to efficiently integrate the TDD approach within our Scala project.

By working through this example, you'll gain practical experience with TDD principles and develop the calculateTotal function in a way that showcases how TDD fosters code quality and robustness.