TDD Process

Process Steps

Step 1: Red Phase

• Write a failing test for the target behavior
• Run the test suite on that specific file
• Gate: Failure must be on the assertion — not a syntax or configuration error
• Checkpoint: Present the test code and failure output before proceeding to implementation

Step 2: Green Phase

• Write the minimal code required to pass the test — nothing more
• Run the test file
• Checkpoint: Present the minimal implementation once tests pass

Step 3: Refactor Phase

• Clean up duplication, naming, class structures, and documentation
• Run the test suite after each micro-change
• Gate: Tests must remain green throughout

Framework Example

RSpec

Failing Test (RED):

# spec/user_spec.rb
RSpec.describe User do
  describe "#full_name" do
    it "combines first name and last name" do
      user = User.new(first_name: "Ada", last_name: "Lovelace")
      expect(user.full_name).to eq("Ada Lovelace")
    end
  end
end

Failure command & output:

$ bundle exec rspec spec/user_spec.rb
...
1 example, 1 failure
Failed examples:
rspec ./spec/user_spec.rb:4 # User#full_name combines first name and last name (NoMethodError: undefined method `full_name')

Minimal Implementation (GREEN):

# lib/user.rb
class User
  def initialize(first_name:, last_name:)
    @first_name, @last_name = first_name, last_name
  end

  def full_name
    "#{@first_name} #{@last_name}"
  end
end

Additional framework examples are available in companion files:

• EXAMPLES_PYTEST.md — pytest (Python)
• EXAMPLES_JEST.md — Jest (JavaScript/TypeScript)
• EXAMPLES_GO_TEST.md — Go testing package

Integration