TDD (Test-Driven Development)

What is TDD?

• A development style where software is implemented by intorducing test cases first
• States of software development
  • Red: All the tests are not passed (some tests are failed)
  • Green: All the tests are passed
  • Refactoring: The codes should be refactored

Basic Steps of TDD

• Step 1: Create a test case for a function. The software status is Red because the function is not implemented yet.
• Step 2: The minimum implementation is done to pass the test case, and the software status becomes Green.
• Step 3: Consider the refactoring of codes while the status of software is kept Green.

Repeat Step 1 though Step 3.

Concept

• Creation of both body and test codes for the system
• Created tests become minimum check programs to ensure the system to run
• The test code is regarded as the definition of done.

Best Practice

• The software under test should be available any time anyone. The time for Red is to be as short as possible.
• The test code is also to be tested. The status is to be Red once.
• The design of codes is considered while the status is Green. The test codes behave as a safety function.

Benefits of TDD

• Development starts from clear and testable specifications.
• Design becomes more modular and robust.
• Code is implemented with testing in mind.
• Test cases serve as up-to-date documentation.
• Tests are maintainable, reusable, and easy to understand.
• "Definition of done" becomes clearer through test coverage.

Summary

• TDD encourages reliable, testable, and clean code.
• Development follows a simple cycle: Red → Green → Refactor.
• The Red state means tests fail (expected after writing a new test).
• The Green state means all tests pass.
• Refactoring is done while the code is Green to improve structure.
• Test code defines the "Definition of Done".
• Tests themselves should be maintainable and clear.