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

bg width:400 right:40%

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. :arrow_right: The time for Red is to be as short as possible.
  • The test code is also to be tested. :arrow_right: The status is to be Red once.
  • The design of codes is considered while the status is Green. :arrow_right: 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.