Welcome back to our course on Test-Driven Development (TDD) using Scala and ScalaTest. In our previous lesson, we introduced the fundamentals of TDD and the Red-Green-Refactor workflow. Now, we will advance our TDD skills by focusing on generalizing solutions and enhancing the complexity of our testing scenarios.

As a brief reminder, TDD involves a repetitive cycle known as Red-Green-Refactor:

• Red: Write a failing test to clarify the new functionality you aim to implement.
• Green: Develop the smallest amount of code needed to make that test pass.
• Refactor: Clean up the code, enhancing its quality while maintaining its functionality and ensuring all tests remain passing.

In this lesson, we will expand upon the sum method, demonstrating how to generalize it while following these TDD principles.

Before we dive into coding, let's review our current setup. You are already familiar with the sum method and its corresponding test in the MathFunSuite:

This existing setup serves as a foundation. Now, we'll focus on expanding your understanding by generalizing the approach using TDD principles. Understanding where you've come from will help ensure future changes enhance our function without straying too far from the core logic.

To embrace the Red phase, let's introduce a new test case that will fail.

Update MathFunSuite to include more input scenarios:

By including a new scenario with new inputs, this step is intentionally set to fail to define our target goal clearly.

Running this test will show that our implementation does not account for varying inputs, prompting us to generalize our solution.

Now, let's transition to the Green phase, where our goal is to ensure all tests pass, including our new one. We can update our sum method to use the generic response because it is the minimal solution.

Rerunning the tests will show:

Success! The Green phase is complete, illustrating how effective writing minimal code to pass tests can be.

Finally, let's advance into the Refactor stage. The sum method is very simple, so there's nothing we can improve with the implementation. However, we have a lot of duplication in our tests.

Let's introduce table-driven testing, which allows for parameterized tests. It makes it easy to add a lot of test cases without duplicating too much test code:

In this refactored test, we use ScalaTest's TableDrivenPropertyChecks to streamline our testing process with predefined test cases. This makes it flexible and easy to extend as requirements evolve.

Additionally, we have utilized the shouldBe matcher to improve test readability and expressiveness. We'll explore more about ScalaTest matchers in an upcoming unit to help you write even more effective tests.

In this lesson, we delved into using TDD to generalize solutions in Scala by:

• Reviewing and examining the initial state of the sum method and its associated test cases.
• Engaging in the Red phase by adding a new failing test to identify necessary functionality improvements.
• Advancing to the Green phase by implementing minimal code changes to pass the new test.
• Moving to the Refactor phase, where we utilized table-driven testing to reduce test duplication and improve maintainability.

Reflect on these processes and apply them to your development tasks. By reinforcing these skills, you'll enhance your ability to produce robust, adaptable Scala code efficiently.