Test Driven Development

Test-Driven Development (TDD) is a computer programming technique that involves writing test cases first and then implementing the code necessary to pass the tests. The goal of test-driven development is to achieve rapid feedback and implements the "illustrate the main line" approach to constructing a program. This technique is heavily emphasized in Extreme Programming.

Practitioners emphasize that test-driven development is primarily a method of designing software, not just a method of testing. The method is also used for removal of software defects.

Test-Driven Development Cycle

1. Write the test

It begins with writing a test. In order to write a test, the developer must understand the specification and the requirements clearly. This is accomplished through use cases and user stories. The design document covers all the test scenarios and exception conditions.

2. Write the code

The next step is to make the test pass by writing the code. This step forces the programmer to take the perspective of a client by seeing the code through its interfaces. This is the design driven part of test-driven development. As part of test calibration, your code should fail the test meaningfully the first time around.

3. Run the automated tests

The next step is to run the automated test cases and observe if they pass or fail. If they pass, the programmer can be more confident that the code meets the test cases as written. If there are failures, the code did not meet the test cases..

4. Refactor

The final step is the refactoring step and any code clean-up necessary will occur here. The test cases are then re-run and observed.

5. Repeat

The cycle will then repeat itself and start with either adding additional functionality or fixing any errors.