A Guide to Test Driven Development (TDD)

May 3, 2024 | Best Practices, Test Automation Insights

For developers who work on many agile projects, test-driven development (TDD) may be something you wish to incorporate into your software development life cycle (SDLC). It’s a way to implement software programming while integrating unit testing, programming, and source code refactoring. Read on to gain a deeper understanding of TDD, its benefits, and tips on incorporating it into your development process.  

🤔 What Is Test-Driven Development? 

The test-driven development process may take some time as it upends traditional development and testing. Developers typically start writing code before designing a validation test. TDD does the reverse, which requires adjusting how you think while coding. 

Instead, you start by writing the unit test. After it inevitably fails, you implement code changes until the test passes. While the adjustment takes some getting used to, using TDD allows you to obtain cleaner lines of code that don’t break after a long period of use.  

Unit tests are tests covering only a small piece of your logic rather than the entire program. It may help to think of them as algorithms, procedures used to solve problems or perform computations.  

Your unit tests should have a predetermined outcome without relying on other calls. Instead of using randomly changing data, it’s best to create a “mock” version that stays the same so that you get an expected result from your test.  

One common test-driven development example is adding a new text field to a web form. You start by writing a test that validates that the user enters only text data. Your test should fail if the user enters a number or special character. Write tests that ensure that nothing else passes validation but text values.  

📌 Core Principles of TDD 

Two fundamental processes make up the test-driven development approach — the red-green-refactor cycle, and simple design and refactoring. Let’s take a look at each.

The Red-Green-Refactor Cycle 

The red-green-refactor cycle compartmentalizes your coding focus into three different phases and consists of the following steps: 

  • Red: Start by writing a test describing the behavior you want to implement in your code. Because you haven’t started writing any code, the test automatically fails. Most testing frameworks reflect this as the color red.  
  • Green: Now, write the minimum code necessary to pass the test. Try to write only enough lines of code required to satisfy the test. Don’t worry about making it optimal or extensible. You’re trying to get past the test, nothing more. Most frameworks reflect the color green to indicate success.  
  • Refractor: Now that you’ve passed your test, improve the application code in ways that don’t change the behavior. Focus on making it cleaner, maintainable, and more efficient. Your refactored code should still pass your written tests. This step keeps your overall codebase manageable without adding to your organization’s technical debt, which is covered later in this guide.  

Simple Design and Refactoring 

Simple design and refactoring emphasize writing efficient, clean, and extensible code.  

Simple design  

Simple design makes code easy to understand, modify, and maintain. It emphasizes clarity over complexity. Characteristics of simple design include: 

  • Using clear and expressive code to communicate its intended effect 
  • Incorporating reusable components and abstractions to reduce duplication 
  • Focusing on modular and cohesive structure, giving each component a clear responsibility 
  • Adding flexibility to accommodate new changes and future requirement updates to avoid the need for extensive modifications 


Refactoring is a technique for improving code structure, organization, and readability without changing its behavior. You make small, controlled changes that eliminate duplication, use robust design patterns, and enhance quality. TDD relies heavily on refactoring during the development cycle.  

After writing your first failed test, you start refactoring when implementing the minimal code needed to obtain a pass. Once you get through the Red-Green section, you start making updates to make your code more straightforward to understand. Developers perform refactoring constantly to ensure the code remains clean and flexible.  

✅ Benefits of Adopting TDD in Software Development 

Let’s review some of the advantages of test-driven development for software builds.  

Improved Code Quality 

TDD encourages developers to write tests that function as specifications for their desired behavior. That clarity around expectations helps make code more precise, which means it’s easier to understand the purpose of every component.  

Another benefit to TDD is that it leads to more modular, loosely designed code. The focus on writing tests first helps with cohesiveness. It also helps developers think through design decisions from the start, leading to better architecture.  

Using TDD leads to the creation of automated tests for regression testing, which catches unintended changes that break existing functionality. This happens much earlier in the development cycle with TDD, keeping codebase changes from introducing new bugs.  

Reduced Errors 

Taking a more disciplined approach to coding that introduces tests from the start provides a safety net. You have an immediate feedback loop that tells you if the code behaves as expected. Catching errors early stops bugs from reaching other parts of your program.  

Tests written for TDD provide precise specifications for how your codebase should function. Defining expectations upfront helps ensure that you cover all detailed requirements during the implementation phase.  

This incremental development method stops the evolution of complicated spaghetti code that’s hard to follow and maintain. Breaking code into more understandable components helps developers focus on better practices that produce more reliable applications.  

Improved Project Management 

Because TDD helps developers catch bugs earlier, it makes it easier to detect and mitigate issues from the start. That greatly reduces the possibility of a bug making it into a later development stage, which might be more costly to fix. Projects end up experiencing fewer delays because of a reduced need to rework issues.  

The acceptance tests produced by TDD increase confidence in the code’s ability to perform, lowering project risk. Writing tests also encourages collaboration between developers, testers, and other stakeholders. Everyone can access a common language to discuss requirements and validate program functionality.  

Agile test-driven development tests also serve as codebase documentation. You can access a real-time illustration of a program’s intended usage and behavior. That gives project managers and non-technical users more understanding of how the system functions. They can use that information to make more informed decisions regarding project scope, priorities, and resource allocation.  

Reduced Costs 

TDD helps improve code quality by catching errors during the development phase. Identifying issues earlier makes fixing bugs less expensive than delaying a project in later stages and sending it back to the developer.  

While developers may need some time to adjust to TDD, regular usage often leads to faster development time by reducing the need to rework code. This helps with more rapid delivery of features and updates, translating into cost savings because less time is needed to complete projects.  

Reduced Technical Debt 

Developers sometimes feel pressured to write code quickly to meet a project deadline. While they may accomplish their immediate goals, those efforts can result in inefficient code that’s hard to manage over the long term. Taking shortcuts like not refactoring can cause technical debt to accumulate quickly.  

Another cause of technical debt is a need for more documentation around legacy code. Developers tasked with making it more workable often face a lack of documentation or the need to remove outdated dependencies and depreciated features and find a replacement. 

📋 How To Start Implementing TDD in Your Development Process 

Before you start using TDD, familiarize yourself with its underlying principles and benefits. Then, start exploring different testing frameworks that support your technology stack. Examples include JUnit for Java test-driven development, NUnit for .Net test-driven development, and pytest for Python test-driven development.  

Once you feel comfortable and have selected your preferred test-driven development tool, you can break the process down into the following sequence.  

1. Add a Test 

Identify the requirement you wish to implement in your code, such as a new feature, bug fix, or modification to existing functionality.  

2. Run to See if It Fails

Write a test that covers the behavior expected from your code. It should fail because the code that supports your requirement does not exist. Run the test to confirm that it fails as expected.  

3. Write Code 

After you get your first failing result, start writing code that covers only the basics to meet the test standards.  

4. Run the Test Again 

Rerun the test to see if it fails. If it does, make the changes necessary to obtain a green result. Keep going until you satisfy the test standards.  

5. Start Refactoring Code 

Once you get your passing result, start refactoring the code to improve factors like design, readability, and efficiency. Focus on keeping the code clean and readable. Stick to development best practices to avoid pitfalls that could increase overall technical debt. Keep making improvements until you are satisfied. 

6. Repeat

Repeat the process for the next requirement once you obtain a green result with your refactored code. Keep going until you have covered everything necessary to complete the development phase.  

⚙️ Embrace TDD With Ranorex 

Ranorex testing tools allow developers to write powerful tests with minimal coding. Our automated platform reduces the need to write many tests manually, speeding up your development process. Contact one of our representatives to learn more about the benefits of making Ranorex part of your process.



Related Posts:

Secure Your Code, Harden Your App, Automate Its Testing

Secure Your Code, Harden Your App, Automate Its Testing

With DevOps practices more popular than ever in software engineering, there has been a push to integrate security, optimization, and frequent testing into the development process. However, as the baseline for what's considered good software evolves, so does the need...

Proof of Principle vs. Proof of Concept: How Are They Different?

Proof of Principle vs. Proof of Concept: How Are They Different?

The terms proof of principle (PoP) and proof of concept (PoC) are often used interchangeably in industries such as technology and research. However, they have distinct meanings and purposes. While both aim to validate ideas or hypotheses, their approaches and scopes...