Test Driven Development (TDD)

Test Driven Development (TDD) - Toolshero

Test Driven Development (TDD): this article provides a practical explanation of Test Driven Development (TDD). The article begins with the definition and general explanation of this concept, followed by a description of the principles on which this method for software development is based. You will also find information on the different phases in this process and its benefits. Enjoy reading!

What is Test Driven Development (TDD)?

Test driven development (TDD) is an approach to software development and one of the most popular testing frameworks where test cases are used to specify and validate what a new piece of code does. In simple terms, for each functionality, a test is written first, followed by implementing and testing the code. Based on the test results, a decision is made whether to keep the code as is or to rewrite it.

The TDD process therefore begins with designing and developing tests for specific functionalities of an application. The TDD framework requires developers to only write new code when a test has failed, to avoid duplicating code.

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TDD is an iterative approach to programming. The framework finds its roots in the principles of Agile and Extreme Programming (XP). As the name suggests, the testing process drives development. This structured approach enables developers to obtain optimized code that is also resilient in the long term.

The American software engineer Kent Beck wrote a book on this method: Test Driven Development: By Example.

Principles of Test Driven Development (TDD)

As mentioned, Test-driven development (TDD) is closely related to the principles of Extreme Programming (XP) and Agile. TDD is even often considered one of the core practices of Extreme Programming and is frequently used in Agile environments to support the principles of iterative development and frequent feedback.

Extreme Programming is a software development methodology that emphasizes communication, simplicity, and feedback, much like TDD. Extreme Programming is intended as a flexible and adaptive methodology, with a focus on delivering high-quality software that meets the customer’s needs.

TDD aligns with the principles of XP: simplicity and feedback. By writing tests in advance and working iteratively, developers can ensure that their code meets the desired requirements and is easy to maintain and adapt. This focus on simplicity and feedback is also reflected in other Extreme Programming practices, such as pair programming, continuous integration, and frequent releases.

TDD is also closely related to the Agile methodology. Agile is an iterative approach to software development that emphasizes collaboration with the customer, flexibility, and adaptability. It is based on the set of principles described in the Agile Manifesto, including regularly delivering working software, responding to change, and valuing individuals and interactions over processes and tools.

The cycle of test-driven development

As indicated, the TDD process is iterative. This means that the process is continuously repeated. Test-driven development (TDD) is a software development process that emphasizes writing automated tests before writing code. It follows a cycle of five phases that ensures that the software is developed and tested incrementally.

1. Add a test

The first phase of TDD involves writing a test and adding it to the code. This test should be small and specific, and test only one aspect of the functionality of the code. The test is designed to initially fail because the code has not yet been written.

2. Running the test

Once the acceptance test has been added, it is run to confirm that it fails. This confirms that the test is working correctly and that the test covers the intended functionality. If the test passes at this stage, it suggests that it may be testing the wrong functionality, or that it is not specific enough.

3. Write code

The next step in the TDD cycle involves writing the minimum code needed to pass the test. The focus is on writing clean, modular, and maintainable code that meets the requirements of the test. The goal is to write the simplest code that meets the test requirements.

4. Test code

Once the code is written, the next step is to run all tests, including the newly added one. If all tests pass, it confirms that the code meets the test requirements. However, if a test fails, the developer will need to analyze the test failure to identify and resolve the problem.

5. Rewrite the code if necessary

If tests fail in the previous step, the last phase of the TDD cycle involves rewriting the code to fix the failing test(s). The code is rewritten to remove duplication, simplify complex code, and improve the overall design of the code. This cycle continues until all tests pass and the code meets the software requirements.

In summary, TDD is a valuable process that helps developers create high-quality code that meets the software requirements. It ensures that the code is incrementally tested, and it helps reduce the time and cost of software development.

Benefits of the test-driven development approach

One of the main benefits of TDD is that it leads to higher code quality. By writing tests first, developers are forced to think about the behavior of their code before writing it. This helps ensure that the code meets the desired requirements, and that the code can be maintained and improved in the future.

In addition, because tests are written for each new piece of functionality, TDD encourages developers to write modular code, making it easier to change and maintain over time.

Another advantage of TDD is that it can shorten development time. Although writing tests upfront may seem like an extra step, it can save time in the long run by catching bugs early in the development cycle. This reduces the time that would otherwise be spent debugging and troubleshooting in a later stage.

Furthermore, because TDD encourages developers to write small, incremental changes, it can help prevent large-scale refactoring that can be time-consuming and error-prone.

Finally, TDD can help increase confidence in the codebase. Since tests are run regularly, and new tests are written for each new piece of functionality, developers can be more confident that changes to the codebase haven’t introduced bugs. This can lead to a more stable and reliable codebase, which is particularly important for applications that require high reliability and uptime.

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It’s Your Turn

What do you think? Do you recognize the explanation of test-driven development? Do you see similarities with the principles of Agile and Extreme Programming (XP)? Do you have tips for going through the different stages of TDD? Do you think testing after every change is crucial, or can testing be done at the end as well?

Share your experience and knowledge in the comments box below.

More information

  1. Astels, D. (2003). Test driven development: A practical guide. Prentice Hall Professional Technical Reference.
  2. Beck, K. (2003). Test-driven development: by example. Addison-Wesley Professional
  3. George, B., & Williams, L. (2004). A structured experiment of test-driven development. Information and software Technology, 46(5), 337-342.
  4. Maximilien, E. M., & Williams, L. (2003, May). Assessing test-driven development at IBM. In 25th International Conference on Software Engineering, 2003. Proceedings. (pp. 564-569). IEEE.

How to cite this article:
Janse, B. (2018). Test Driven Development (TDD). Retrieved [insert date] from Toolshero: https://www.toolshero.com/information-technology/test-driven-development/

Original publication date: 05/24/2023 | Last update: 05/08/2024

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Vincent van Vliet
Article by:

Vincent van Vliet

Vincent van Vliet is co-founder and responsible for the content and release management. Together with the team Vincent sets the strategy and manages the content planning, go-to-market, customer experience and corporate development aspects of the company.


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