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Why Test Driven Development Matters: Best Practices to Implement TDD

Software Development September 27, 2023

Test driven development (TDD) has become a widespread software development practice, and it is often used in conjunction with other agile development methodologies such as Scrum and Kanban.

The term “test driven development” (TDD) was coined by Kent Beck in the early 1990s. In his book “Extreme Programming Explained: Embrace Change”, he outlined the basic steps of TDD:

  • Write a failing unit test.
  • Write the minimum amount of code to make the test pass.
  • Refactor the code to improve its design.
  • Repeat steps 1-3 until all the desired functionality is implemented.

There is a growing body of evidence that suggests that TDD can help improve the quality of software, reduce defects, and shorten development cycles. A study by Microsoft found that TDD projects had a 60-90% drop in the density of defects. (Source)

If you are looking to witness the same drop in defect density in your software development projects, you are at the right place.

In this blog, we will delve into what test driven development is, its process, benefits top frameworks, examples, and best practices to implement TDD in your project.

Here we go!

What Is Test-Driven Development (TDD)?

Test-Driven Development (TDD) is a method in software development. Instead of writing code first, developers begin by creating tests. The main goal is to confirm that the code works correctly by testing it against these pre-established criteria. TDD follows a repetitive process called the “Red-Green-Refactor” cycle:

  • Red: Write a failing test case. This test represents a specific requirement or functionality you want to implement.
  • Green: Write the minimum amount of code required to make the failing test pass. This code may be incomplete or inefficient.
  • Refactor: Refine the code, making it more efficient, readable, and maintainable while ensuring that all tests still pass.

This process continues iteratively, helping developers build a robust and well-tested codebase.

Benefits Of Test Driven Development

Benefits Of Test-Driven Development

Reddit users share their experience using TDD

The benefits of Test-Driven Development are numerous:

Better Code Quality

TDD encourages developers to create well-organized and structured code, which makes it easier to manage and maintain.

It helps in addressing issues early, which prevents the accumulation of technical problems in the software, keeping it more manageable.

Increased Development Speed

Test-driven development provides swift feedback by detecting problems early in the development process. This accelerates development because issues are identified and fixed promptly.

With Test driven development, developers can confidently make changes or add new features without worrying about breaking existing functionality, which can speed up the development process.

Improved Team Collaboration

Test driven development promotes a shared understanding of requirements among developers, testers, and other team members, reducing misunderstandings.

It encourages close collaboration between developers and testers, leading to more robust and well-tested software.

Boosted Confidence

TDD allows developers to make changes to the code with confidence because they can rely on existing tests to quickly catch any issues, making the codebase better.

It helps teams predict how the software will behave more accurately, reducing uncertainties in project timelines.


Test cases serve as practical examples of how the code is supposed to work, making it easier for current and future developers to understand and use the software.


TDD integrates well with Continuous Integration and Continuous Deployment (CI/CD) pipelines, automating testing and allowing for frequent, reliable software releases.

Customer Satisfaction

Test-driven development contributes to delivering more stable and reliable software to customers, reducing the chances of critical issues in production and leading to higher user satisfaction.

Cost Efficiency

Finding and fixing problems early in development is generally less expensive than addressing them later. TDD can lead to cost savings by reducing the need for extensive debugging and rework.

Incorporating Test-Driven Development into your software development process can provide various advantages, such as better code quality, faster development, and improved collaboration among team members. As a software testing company, we emphasize the benefits that make TDD a valuable practice for building dependable software.

Improve your custom software with Test-Driven Development!

Key 5 Steps to Implementing Test Driven Development

Steps to Implementing Test Driven Development

The key 5 steps of implementing test-driven development (TDD) are:

Step 1: Write a Test That Fails (Red Phase):

Start by identifying a specific thing you want your program to do or a new feature you want to add.

Create a test that describes what you expect the program to do, even though the code to make it happen doesn’t exist yet.

The test should fail initially because the code hasn’t been written to meet those expectations.

Step 2: Write the Simplest Code to Make the Test Pass (Green Phase):

Write the most basic code required to make the failing test pass. This usually means creating a function, defining variables, or writing fundamental logic.

Don’t worry too much about making the code perfect or efficient at this stage; the main goal is to get the test to work.

Step 3: Improve the Code (Refactor Phase):

After the test passes, take time to review and enhance the code. This could involve making it cleaner, faster, or easier to understand. Ensure that the code follows coding standards and best practices.

Run the tests again to confirm that your changes haven’t introduced new issues. All tests should still pass.

Step 4: Run All Tests (Green Phase Again):

Before moving on to new work or changes, run all the tests, including the existing ones, to make sure your modifications haven’t broken any previously working parts of the program.

If any tests fail, fix the problems immediately and ensure that all tests are passing again before proceeding.

Step 5: Repeat the Process (Red-Green-Refactor):

Go back to Step 1 and repeat the cycle for the next thing you want your program to do or the next feature you want to add.

Write a test first, create the code to make it work, and then improve the code as needed.
Continue this iterative approach until you’ve implemented all the desired functionality or features.

TDD encourages a systematic approach to programming, where you ensure your code works correctly from the very beginning, making it easier to maintain and less prone to errors as you build upon it.

What Is Test-Driven Development In Agile?

In Agile, Test-Driven Development (TDD) is about beginning with a test that checks what your code should do. This test will fail because there’s no code yet. Then, you create the code to make that test pass. This process ensures your code works correctly and fits with Agile’s incremental and quality-centric philosophy.

Test-driven development (TDD) seamlessly aligns with Agile methodologies for several key reasons-

  • Incremental Progress: Agile practices emphasize breaking software development into small, manageable steps. TDD naturally complements this by insisting on writing tests that initially fail. This compels developers to tackle problems incrementally and craft code only as needed to pass those tests.
  • Testing Priority: Agile processes prioritize testing throughout the development cycle. TDD goes hand-in-hand with this philosophy as it mandates writing tests before writing the actual code. This ensures that the code is not only functional but also meets the project requirements.
  • Enhanced Code Quality: TDD is a powerful tool for elevating code quality. It encourages developers to create clear and concise code and catches and rectifies defects early in the development process, leading to significant time and cost savings.
  • Simplified Maintenance: By providing a clear set of tests that define the expected behavior, TDD makes software easier to maintain. This is especially beneficial when adding new features or addressing issues since the tests serve as a roadmap for code modifications.

In practical terms:

In a Scrum team, TDD can be applied to introduce new features or address bugs. The team starts by formulating tests that outline the desired feature or problem resolution, then proceeds to develop the code to meet these test criteria. Lastly, they refine the code for readability and maintainability.

In an Extreme Programming (XP) team, TDD is the standard approach for developing all new code. The process kicks off with the creation of failing unit tests for each new method or class.
Subsequently, the code is written to satisfy these tests, followed by code refinement to enhance readability and maintainability.

Regardless of the specific Agile methodology employed, TDD remains a valuable practice to ensure the development of high-quality software.

Top Test-Driven Development Framework


JUnit is a unit testing framework for Java. It is one of the most popular TDD frameworks and is used by many large companies, including Google and Amazon. JUnit is easy to use and has a large community of users and contributors.


TestNG is another popular TDD framework for Java. It is similar to JUnit, but it offers some additional features, such as support for data-driven testing and parallel execution of tests.


Pytest is a Test-driven development framework for Python. It is a very flexible framework that can be used for unit testing, integration testing, and acceptance testing. Pytest is easy to learn and use, and it has a large and active community.


Mocha is a TDD framework for JavaScript. It is easy to use and has a large community of users. Mocha is also a good choice for testing front-end applications.


RSpec is a TDD framework for Ruby. It is very expressive and makes it easy to write clear and concise tests. RSpec is also a good choice for testing APIs.

These tools provide the infrastructure and utilities needed to write and run tests effectively, making it easier for developers to implement Test-driven development in their Agile development processes.

Test-Driven Development (TDD) Examples

The following are some examples of test-driven development:

Email Sending Module

Suppose you’re developing an email-sending module for a larger application. Start by writing tests to verify that emails can be composed correctly and sent to recipients. You can create test cases for different email formats, and attachments, and handle failed email deliveries. Once the tests are defined, implement the email-sending functionality to pass the tests.

Flight Booking System

For a flight booking apps, start by writing tests to verify that users can search for flights, book seats, and receive confirmation emails. Create test cases for fully booked flights, seat availability, and handling booking cancellations. Implement the booking system based on these test cases.

Inventory Management System

If you’re building an inventory management system for a retail business, use TDD to ensure that products can be added, updated, and removed from the inventory. Write tests for scenarios like adding out-of-stock items, updating product quantities, and generating inventory reports. Then, develop the code to manage the inventory based on these test cases.

TDD Vs. Traditional Testing

Test-driven development (TDD) and traditional testing are two different approaches to software testing. TDD is an iterative approach where the developer writes a failing unit test before writing the code that makes the test pass. This ensures that the code is always tested and that new features do not break existing code.

Traditional testing, on the other hand, is a more traditional approach where the developer writes the code and then tests it after the fact.

Let’s check out the differences :

Order of development

Test-driven development: In TDD, you begin by creating tests that outline how your code should function. These tests define the expected behavior of your code. Then, you proceed to write the actual code to meet the requirements set by these tests. In essence, you establish a comprehensive set of tests upfront before coding begins.

Traditional Development: In the traditional development approach, the usual sequence involves writing code first, without initial tests. After writing the code, tests are subsequently crafted to check and validate the code’s functionality. In some cases, tests may not be created at all or may be created as an afterthought once the development phase is complete.


Test-driven development: TDD encourages small, iterative cycles of development. You write a test, make it pass with the minimum amount of code, and then refactor if necessary. This cycle repeats until the desired functionality is achieved.

Traditional development: In the traditional approach, development often progresses linearly, with testing as a separate phase at the end. This can lead to longer development cycles and potentially more significant issues when bugs are discovered late in the process

Bug Detection

Test-driven development: TDD aims to catch bugs early in the development process by writing tests that verify the correctness of the code. This can lead to fewer bugs in the final product.

Traditional development: Bugs may be discovered later in the development process, which can be more costly to fix.


Test-driven development: Test-driven development can encourage better software design because you’re forced to think about how to test your code from the start. This often leads to more modular and loosely coupled code.

Traditional development: In the traditional approach, the focus might be on getting the code to work initially, and design considerations can be secondary.

Developer Productivity

Test-driven development: test driven development can initially feel slower because you’re writing tests before writing code. However, it can lead to higher productivity over time by reducing debugging and maintenance efforts.

Traditional development: The traditional approach may seem faster at the outset, but it can lead to more time spent on debugging and fixing issues later.

Best Practices for Test-Driven Development (TDD)

Red-Green-Refactor Cycle:

In Test-driven development, you start by writing a failing test, which outlines the desired behavior of your code (Red).

Next, you write the minimal amount of code needed to make the test pass (Green).
Once the test passes, you can safely refactor your code to improve its design, structure, and performance (Refactor). This cycle is repeated iteratively throughout development.

Focused Tests:

Test-driven development encourages you to write small, focused tests that assess one specific aspect of your code’s behavior. These tests should be isolated from one another to pinpoint issues quickly.

Automated Testing:

Automation is crucial in test driven development to ensure that your tests can be executed frequently and consistently without manual effort. Tools like JUnit, NUnit, or pytest automate the testing process.

Test Coverage:

Test coverage measures the percentage of your code that is exercised by tests. While aiming for 100% coverage may not always be practical, it’s important to prioritize testing critical and complex code paths.

Descriptive Test Names:

Descriptive test names serve as documentation for your code. A well-named test should clearly indicate what behavior it is testing, making it easier for developers to understand the purpose of the test.

Continuous Integration (CI):

CI systems like Jenkins or Travis CI automatically build and test your code whenever changes are committed to the version control system. This helps catch issues early and ensures codebase integrity in test driven development.


Refactoring is the process of restructuring code to improve its quality without changing its external behavior. TDD provides a safety net for refactoring by ensuring that any regressions are quickly identified and addressed.

Boundary Testing:

In Test driven development, it’s essential to test not only the “happy path” but also boundary conditions and error scenarios. Robust testing helps ensure that your code handles a variety of situations correctly.

Simplicity in Code and Tests:

Keeping code and tests simple reduces complexity and the likelihood of introducing bugs. Strive for elegant, straightforward solutions rather than overly complex ones.

Collaboration and Learning:

Collaboration between dedicated developers, testers, and stakeholders is key to ensuring that tests align with the desired functionality of the software. Continuous learning and improvement of testing practices based on feedback and experience are fundamental to test-driven development success.

In the software development process, achieving high-quality products necessitates the inclusion of debugging and optimization. When integrated effectively, the Test driven development (TDD) approach offers a multitude of advantages, notably in terms of long-term cost-effectiveness and the delivery of tangible value to businesses.

Wrapping up,

In conclusion, Test driven development (TDD) is a game-changer in software development. By writing tests before code, TDD ensures higher code quality, faster development, and improved collaboration. It seamlessly integrates with Agile and offers numerous benefits, including early bug detection, better design, and long-term productivity.

TDD’s Red-Green-Refactor cycle, automated testing, code coverage, and collaboration are key practices for success. As a software development company, we at Zealous embrace TDD to build better, more reliable software, satisfying customers and saving time and resources in the long run.

Improve your custom software with Test-Driven Development!

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    Pranjal Mehta

    Pranjal Mehta is the Managing Director of Zealous System, a leading software solutions provider. Having 10+ years of experience and clientele across the globe, he is always curious to stay ahead in the market by inculcating latest technologies and trends in Zealous.


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