Why Test-Driven Development (TDD)


What if you could use effective testing to develop a better, more polished app? Wouldn’t that be great?

With test-driven development (TDD), developers create and automate tests that validate the functionality of the software they are coding. They write only the code that gets validated in order to keep it clear and simple, eliminate bugs, and speed up the development process.

TDD has been around for over two decades now. It was initially associated with extreme programming, which aims to maximize software quality and responsiveness. In recent years, however, it has grown in popularity as a standalone approach to improving the productivity of development teams and generating better code.

In this article, you’ll learn more about the features and benefits of TDD and what projects it’s best suited for. Let’s get right on to it.

Understanding Test-Driven Development

TDD promotes a test-then-code approach. It’s based on the idea that if developers use test cases before writing functionality, they can create better software and, often, complete the project faster. This approach is different from normal software testing, where they generate the code first and only then test it.

TDD developers use test cases before they write a single line of code. This approach encourages them to consider how the software will be used and what design it needs to have to provide the expected usability. Once a test fails, developers understand what needs to be changed and they refactor the code, that is, they rewrite it to improve it without altering its function.

TDD focuses on the code necessary to pass the test, reducing it to essentials. It takes the test unit, or the smallest bit of functionality, as its basis. It’s a bit like building a house brick by brick—no brick is laid down before it’s tested, to make sure it’s sound and that it’s an integral part of the design.

TDD is compatible with the Agile methodology. While Agile focuses on the overall development process, TDD dictates how code gets written. You can combine the benefits of both methodologies to develop high-quality software using test-then-code and short development cycles or sprints.

Benefits of Test-Driven Development

What exactly makes TDD a good choice for software development? Let’s review the key benefits it has to offer to understand what its strengths are and where it’s best employed.

Develop highly usable software

TDD shifts the focus from implementation to the uses of the software. Through its test-first approach, it gives developers the opportunity to consider more carefully the usability challenges users are likely to face. Software built using the TDD approach is inherently usable—otherwise, it simply wouldn’t pass unit testing.

Reduce bugs

Tests ensure that the code stays focused and clear during each stage of development. Automated tests, for example, can highlight mistakes and their impact on the system, which in turn enables developers to detect bugs and other problems that arise as a result of the changes they have most recently made to the code. It becomes easier for them to create software that is solid and works as intended.

Identify functionality issues

With TDD, it’s easy to spot functionality issues even as the software is being developed, which allows for these to be more quickly addressed. When you need to build an app that’s fully functional from the first release, TDD can help you ensure your app achieves its purpose.

Avoid code duplication

The codebase gets cleaned up constantly through refactoring, making room for new code to be added. This process can tighten up the code and place it where it belongs in the codebase. The result is a tidy codebase free from unnecessary duplication, which makes the software easier to tweak and maintain.

Simplify code

TDD requires developers to write code in response to test requirements. This approach promotes the simplification of code. It can prevent excess code and helps keep the codebase streamlined and easy to use. There are no doors left open for superfluous code to creep into the software.

Check the quality of the code

Tests create quality metrics for the code. The team of developers can use TDD to effectively determine how good the code is. In this way, they can develop more consistent code and fix any cracks they spot in it.

Create extensible software

TDD encourages developers to build software using small units of testable code. This modular approach to software development contributes to creating software that’s more flexible and extensible than that built using other methodologies.

Provide quick feedback

Fast iterations mean that developers can receive feedback from clients more quickly than with traditional approaches to software development. They can then use this feedback to craft a more polished piece of software. Clients also benefit. They can choose to be more involved in the development project and review iterations more frequently.

Create up-to-date code documentation

Other developers can use completed tests as usage examples for the code, allowing them to become familiar with it faster. This can make the project more friendly for developers other than those who build the code from the ground up. For long-term projects which may pass through multiple hands, this documentation can be valuable.

Shorten the development time to market

The test-and-code approach increases the productivity of the development team by focusing their energy on passing tests, that is, accomplishing goals. TDD enables you to develop a functional piece of code for end-users in a shorter time span than many other programming practices. This can be a major advantage in today’s competitive software market, where app availability is one of the key factors that determine success.

Is Test-Driven Development Right for Your Project?

You can use TDD for both new software and legacy software projects. When applied to legacy software, TDD uses tests to address bugs separately in a way that enables you to resolve them one by one.

One thing to note is that TDD takes one unit of code at a time as its starting point. For very sophisticated software projects, multiple tests may be required to validate each unit of code before writing it. TDD is only as effective as the tests used to move the project into the coding phase. If the testing is not effective or allows bugs to creep in which are then not spotted and resolved, it may undermine the foundation of the software that’s being built.

Test-driven development is great for:

  • Greenfield software projects, e.g. developing an app from the ground up for a new platform without any constraints.
  • Projects that focus on functionality rather than on the bells and whistles.
  • Projects that require a short implementation time.
  • Long-term software projects that require modulation to facilitate extensibility and continuous development.
  • Projects that need to be optimized in terms of costs and features—that is, where the aim is to get the best functionality possible given the available budget.

But what about the limitations of TDD? What do these say about the range of software you can develop with this programming practice?

  • TDD is not meant to provide full functional testing such as database-reliant software may require. Separate integration testing and compliance testing will be required.
  • TDD calls for clear requirements and that the developer understands them—otherwise, unit testing may not be effective.
  • Running a large number of tests can take time and increase the costs of the project. This can happen with highly complex apps.

Ultimately, it’s important to consider the aims of the project before deciding whether test-driven development is the ideal strategy for it. For many software projects, the answer will be yes, but even then, it’s good to confirm this with your software development company to ensure you’re advancing confidently in the right direction.

Final Thoughts

Test-driven development can help you build software that’s reliable, fully usable, and easy to extend with new features. It comes with a short feedback loop and focuses on what’s important, which can help you optimize your costs.

Whether you’re kickstarting a new software project or need to redesign legacy software into a modern and effective solution for your business, TDD can be the right approach for you. Your software development company should understand the benefits of TDD and help you decide whether it’s the right choice for your project.

In the end, remember that while TDD proposes a better way to develop apps, it doesn’t magically solve all software issues. Having clear requirements in place and communicating them clearly remains crucial.