What is Test Driven Development (TDD) : Approach & Benefits

The evolution of Agile development has introduced many pragmatic practices for delivering quality software at high speed. Test-Driven Development (TDD) is one such practice that is now recognized as an efficient approach that drives positive results.

This article describes the TDD approach in detail along with its stages and benefits in software development.

What is Test Driven Development (TDD)?

In layman’s terms, Test Driven Development (TDD) is a software development practice that focuses on creating unit test cases before developing the actual code. It is an iterative approach that combines programming, the creation of unit tests, and refactoring.

The TDD approach derives its roots from the Agile manifesto principles and Extreme programming. As the name suggests, the test process drives software development. Moreover, it’s a structuring practice that enables developers and testers to obtain optimized code that proves to be resilient in the long term.

In TDD, developers start creating small test cases for every feature based on their initial understanding. The primary intention of this technique is to modify or write new code only if the tests fail. This prevents duplication of test scripts.

Three phases of Test Driven Development

1. Create precise tests: Developers need to create precise unit tests to verify the functionality of specific features. They must ensure that the test compiles so that it can execute. In most cases, the test is bound to fail. This is a meaningful failure as developers are creating compact tests based on their assumptions of how the feature will behave.
2. Correcting the Code: Once a test fails, developers need to make the minimal changes required to correct the code so that it can run successfully when re-executed.
3. Refactor the Code: Once the test runs successfully, check for redundancy or any possible code optimizations to enhance overall performance. Ensure that refactoring does not affect the external behavior of the program.

The image below represents a high-level TDD approach towards development:

Image source

Also read: TDD vs BDD vs ATDD

How TDD fits into Agile development?

Agile development demands regular feedback to develop the expected product. In simple terms, one can also term Agile development as Feedback Driven Development.

There’s a high probability that project requirements may change during the development sprint cycle. To deal with this and to build products aligned with the client’s changing requirements, teams need constant feedback to avoid dishing out unusable software. TDD is built to offer such feedback early on.

TDD’s test-first approach also helps mitigate critical bottlenecks that obstruct the quality and delivery of software. Based on the constant feedback, bug fixes, and addition of new features, the system evolves to ensure that everything works as intended. TDD enhances collaboration between team members from both the development and QA teams as well as with the client. Additionally, as the tests are created beforehand, teams don’t need to spend time recreating extensive test scripts.

Benefits of Test Driven Development (TDD)

1. Fosters the creation of optimized code.
2. Helps developers better analyze and understand client requirements and request clarity when they are not adequately defined.
3. The addition and testing of new functionalities become much easier in the latter stages of development.
4. Test coverage under TDD is much higher compared to the conventional development models. This is because the TDD focuses on creating tests for each functionality right from the beginning.
5. Enhances the productivity of the developer and leads to the development of a codebase that is flexible and easy to maintain.

Frameworks for Test Driven Development

Based on unique programming languages, there are multiple frameworks that support test driven development. Listed below are a few popular ones.

1. csUnit and NUnit – Both are open source unit testing frameworks for .NET projects.
2. PyUnit and DocTest: Popular Unit testing framework for Python.
3. Junit: Widely used unit testing tool for Java
4. TestNG: Another popular Java testing framework. This framework overcomes the limitations of Junit.
5. Rspec: A testing framework for Ruby projects

The process of delivering quality products requires not just debugging but also demands optimization in the development process. When incorporated correctly, the TDD approach provides numerous benefits, particularly in terms of bringing cost-efficiency in the long run and delivering true value to businesses.