Generalization in TDD with Ruby and RSpec

Welcome back to our course on Test-Driven Development (TDD) using Ruby and RSpec. 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 a simple sum function, demonstrating how to generalize it while following these TDD principles.

Before we dive into coding, let's review our current setup. We are going to create a simple sum method and tests associated with it in Ruby.

math_spec.rb

require './math'

RSpec.describe 'sum method' do
  it 'adds two numbers correctly' do
    expect(sum(2, 3)).to eq(5)
  end
end

math.rb

def sum(a, b)
  5
end

This 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 math_spec.rb to add an additional input scenario:

math_spec.rb

require './math'

RSpec.describe 'sum method' do
  it 'adds two numbers correctly' do
    expect(sum(2, 3)).to eq(5)
  end

  it 'adds two other numbers' do
    expect(sum(5, 6)).to eq(11)
  end
end

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

Running this test with RSpec will demonstrate a failure, indicating the need for new functionality.