Software Development

The Essentials of Test-Driven Development





Software Development


The Essentials of Test-Driven Development

Published: 2023/11/06

6 min read

What is Test-Driven Development

Imagine if developers had an organized and systematic approach to coding that allowed them to detect and resolve bugs early in the development process. The good news is that such an approach, test-driven development (TDD) exists. If you’re familiar with software development, you may have heard of TDD before, as it has gained widespread recognition. However, have you ever asked yourself, ‘What exactly is TDD, and what does it entail?’ Put simply, TDD stands for Test-Driven Development, a custom software development that involves writing tests before writing code. Test-driven development for embedded systems ensures leads are well-tested and that software is dependable. Aspiring coders might still ask themselves, what is the difference between Test-first development and TDD? Well, the key difference is that test-first development (TFD) is a general approach to writing tests before code, whereas test-driven development (TDD) specifically follows a cyclic process of Red-Green-Refactor in short iterations. Nevertheless, why is TDD important, and why should developers learn about it?

For one thing, test-driven development offers several advantages over other approaches. It gives developers greater confidence that their software functions correctly and continues to do so as it evolves. The TDD methodology systematically emphasizes the creation of automated tests before writing the actual code. If you are not familiar with TDD, then you might have heard of BDD, behavior-driven development. But how do we understand TDD vs BDD? TDD and BDD are complementary methodologies. Whereas TDD focuses on testing code, BDD emphasizes specifying and testing behavior. BDD is a methodology that extends the principles of test-driven development (TDD) by focusing on the behavior and expected outcomes of a software system from the user’s perspective. Now that we’ve answered, “What is test-driven development?”, let’s look at its phases.

Phases of Test-Driven Development

TDD practices are often integrated into Agile development methodologies with help from a dedicated software development team. With that said, what is the TDD process in Agile? The most straightforward answer would be that the TDD process in Agile involves writing failing tests, writing the minimal code to make them pass and then refactoring to ensure software quality and maintainability. This TDD cycle is a cyclical, iterative process of integrating coding, testing and design. Let’s look at the specific phases to understand it better:

Writing a Failing Test (Red)

The cycle begins by creating a new test that captures a specific behavior or functionality you want to implement. The undeveloped software caused the initial failure of this test. This “Red” phase sets the target for the new code to meet. With TDD in Agile, you define a test that captures the behavior you want to implement. This test is intentionally designed to fail since you must still write the corresponding code. In this case, the test is designed to fail because we still need to implement more functions.

Writing Code to Make the Test Pass (Green)

After defining the failing test, a developer writes the minimal code necessary to pass the test successfully. This “Green” phase is where the actual implementation of the desired functionality occurs. It’s important to note that the goal here is not to write complex or exhaustive code, but just enough to pass the test.

Refactoring Code (Refactor)

In the “Refactor” phase, the code is reviewed and enhanced without changing its external behavior. This can involve making the code more readable, efficient and maintainable. Notably, the existing tests must continue to pass after these refactorings, while ensuring that code quality remains high. Refactoring should not break the current tests. By following this iterative process, test-driven development in Agile becomes effortless.

Examples of Test-Driven Development

In “Test-Driven Development by Example,” Kent Beck demonstrates the TDD methodology with practical examples, emphasizing the creation of tests before the code. TDD prioritizes test writing in the development process and provides a structured approach to constructing reliable and efficient software. A typical TDD example involves initiating a failing test that examines a particular code function, then proceeding to code the function to achieve test success and finally optimizing the code for efficiency. Here are some TDD scenarios with examples of practical applications:

Web Application Testing:

Scenario 1: Apply TDD in a web application with a login feature. Write a test for user authentication, which should initially fail. Implement the login feature to make the test pass. Then, add more tests for various authentication scenarios, such as valid user or invalid password and develop features accordingly.

Game Development:

Scenario 2: In game development, create a game with character movement and collision detection. Develop tests for character movement and collision detection, ensuring the initial tests fail. For instance, a test to guarantee that the character cannot pass through walls. Implement this feature, verify it passes and continue with additional tests to cover various game mechanics.

API Development:

Scenario 3: If you’re building an API to manage a database of products, a TDD approach is beneficial. Write tests for fundamental API operations like creating, reading, updating and deleting products, ensuring they fail initially. Then, implement the API endpoints to make the tests pass. Gradually add more tests to address edge cases and extend the functionality.

These examples demonstrate how TDD can be applied across various domains and types of software development to ensure that code is well-tested and reliable from the outset.

Benefits of test driven development

TDD software development results in more reliable and maintainable software due to the rigorous testing and iterative nature of the process. Test-driven development offers several benefits and provides a wide array of advantages for both individual developers and development teams:

Reduced Defect Rates

TDD significantly reduces defect rates by catching issues early in the development process and prevents bugs from making their way into the final product.

Efficiency Gains

Although TDD may require an initial development effort, it often reduces effort in the project’s final phases – saving time and resources.

Improved Code Design

TDD encourages well-structured and maintainable code, resulting in better technical metrics and more manageable codebases.

Faster Innovation

TDD fosters a culture of rapid innovation by allowing developers to make changes and add new features to their codebase confidently.

Cost Reduction

TDD promotes cost-efficient code by encouraging modularity and loose coupling, reducing maintenance and extension costs.

These top 5 benefits make Test-Driven Development a valuable approach for developers and development teams, leading to improved software quality and efficiency.

Best practices of test driven development

TDD in software engineering is a best practice that ensures the creation of robust and thoroughly tested software that align with industry standards and quality assurance practices. Nevertheless, common pitfalls exist, such as infrequent test runs, poor test suite maintenance and partial adoption of TDD. That’s why you should adopt best practices for TDD.

Other key practices for successful TDD implementation include obtaining buy-in from project leadership, ensuring the development team understands TDD, running all tests in the development pipeline and measuring the value gained from implementing TDD. This kind of development in software engineering promotes the creation of tests before writing code to guarantee the correctness and reliability of the software product. According to “The Three Rules of Test-Driven Development” by Robert C. Martin, in TDD programming, you should:

  • Write production code solely to fulfill a failing unit test,
  • Craft a unit test sufficient to fail, including handling compilation failures,
  • Write only the necessary production code to pass the single failing unit test.

In essence, Rule #1 emphasizes writing tests first to define the required system behavior, Rule #2 encourages incremental progress with constant feedback at each line of code and Rule #3 stresses the importance of writing just enough code to make the failing test pass. These rules guide the practice of Test-Driven Development.


As a software development methodology, TDD testing is great for creating automated tests to verify the functionality of your code as it emphasizes its test cases before you write the code. The best part is that writing perfect tests is optional. The “Red-Green-Refactor” cycle continues as you add more tests, implement more features and maintain the quality of your code. So, while TDD may seem slow at first, it significantly improves software quality, prevents bugs and facilitates code changes. It also reduces defect rates and increases potential cost savings in the initial development effort. What’s more, it enhances the design and technical quality of the software, even though you might encounter challenges such as issues with test execution, overly large or trivial tests and tests for trivial code. You can build reliable and robust software while maintaining confidence that your code works as intended.

Software Mind understands your test driven development in software engineering needs. Through software development outsourcing, we can help your organization build a robust product. Contact one of our specialists to explore how we can improve your solutions and accelerate software delivery lifecycles.

About the authorSoftware Mind

Software Mind provides companies with autonomous development teams who manage software life cycles from ideation to release and beyond. For over 20 years we’ve been enriching organizations with the talent they need to boost scalability, drive dynamic growth and bring disruptive ideas to life. Our top-notch engineering teams combine ownership with leading technologies, including cloud, AI, data science and embedded software to accelerate digital transformations and boost software delivery. A culture that embraces openness, craves more and acts with respect enables our bold and passionate people to create evolutive solutions that support scale-ups, unicorns and enterprise-level companies around the world. 

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