Learn what Test-Driven Development (TDD) is and why it’s essential for high-quality software. We cover the Red-Green-Refactor cycle and explain when and why TDD is used. Crucially, we detail what a Project Manager needs to know about TDD to reduce bugs and manage technical debt.
This video is safe for viewing in the workplace.
This is learning, so, sit back and enjoy
Test-Driven Development
Test Driven Development (TDD) is a software development methodology where developers write automated tests before writing the actual production code. This might sound counterintuitive at first—how can you test something that doesn’t exist yet? However, this reversal of the traditional approach is precisely what makes TDD powerful.
Software engineers develop code, to pass the tests they know it needs to pass. For project managers, you need to understand its benefits, its alternatives, the appropriate contexts for its use, and the project management considerations that come with adopting TDD practices.
The Test-Driven Development Process
The TDD process follows a simple three-step cycle known as Red-Green-Refactor.
- First, developers write a test for a specific piece of functionality that doesn’t yet exist. They then run the test and watch it fail (since the function is not implemented yet)
[Red—the test fails]. - Next, they write the minimum amount of code necessary to make that test pass. They re-run all tests to demonstrate a pass.
[Green—the test succeeds]. - Finally, they refactor the code to improve its structure and readability while ensuring all tests still pass
[Refactor—clean up without breaking functionality]. We have a video on Refactoring
This cycle repeats continuously throughout development, with each new feature or requirement beginning with a new test.
The key distinction of TDD is that tests aren’t an afterthought or quality assurance step—they’re the starting point and driving force of development.
Each test represents a specification of what the code should do, transforming requirements into executable documentation that validates the software works as intended.
What Are the Alternatives to Test-Driven Development?
Several approaches to testing and development exist alongside TDD, each with different philosophies about when and how testing occurs.
Test-last development: Code first, then add tests after. This is common but tends to yield fewer tests, weaker design feedback, and higher defect rates.
Exploratory testing: Skilled testers probe the system without pre-written scripts to find edge cases. Excellent for discovering unknown risks; not a replacement for automated unit tests.
Manual QA cycles: Human testers verify features at the end of a sprint or release. Valuable for usability and system checks; costly and slow for frequent change.
BDD/ATDD (Behaviour/Acceptance Test-Driven Development): Write “Given–When–Then” acceptance tests with business stakeholders. Often complements unit-level TDD rather than replaces it.
Traditional Testing is the most common alternative, where developers write code first and then create tests afterward, if at all. Quality assurance teams often handle testing in a separate phase after development is complete. While this approach feels more natural to many developers, it frequently results in insufficient test coverage, as testing becomes a chore rather than an integral part of development.
Move fast coding without tests: Rapid initial velocity but creates technical debt, brittle code, and high later costs. Similarly, No Formal Testing Process still exists in some organizations, where testing happens ad-hoc or not at all. This approach inevitably leads to costly bugs discovered in production that can have major operational impacts.
When and Why is TDD Used?
TDD excels in projects where code quality, maintainability, and reliability are paramount. It’s particularly valuable in complex systems where changes in one area might unexpectedly break functionality elsewhere, in projects with long lifecycles where code will be maintained for years, and in teams where multiple developers work on the same codebase.
TDD is most commonly used in:
- Long-lived and high-reliability systems where quality is paramount.
- Agile environments where requirements evolve frequently.
- Projects with complex business logic that demand stability and high reliability. Here, early bug detection and reduction of defects are critical.
- Continuous delivery: TDD feeds CI/CD pipelines with trustworthy, fast tests.
- Teams aiming to improve codebase documentation and test coverage. Proponents of TDD maintain that code that is testable generally has a better structure, so TDD tends to generate better structured code. We call this Test Driven Design.
Why Organizations adopt TDD
Organizations adopt TDD for several compelling reasons.
- Improved code structure and maintainability, since developers write modular and testable code. It dramatically reduces the number of bugs that reach production. When developers write tests first, they think through edge cases and potential failures before committing to an implementation approach. This proactive mindset catches problems early when they’re cheapest to fix. TDD code also tends to have fewer unnecessary embellishments, as they would have to be tested to exist.
- Immediate feedback so that defects are identified and fixed early in the process.
- TDD creates living documentation. Unlike traditional documentation that quickly becomes outdated, tests always reflect the current behavior of the system. New team members can read tests to understand what the code does and why, accelerating onboarding and knowledge transfer.
- TDD enables fearless refactoring. Developers can improve code structure, performance, and readability with confidence because comprehensive test suites immediately reveal if changes break existing functionality. This prevents the code rot that plagues many projects over time.
TDD isn’t appropriate for every situation. Highly experimental projects where requirements change rapidly and therefore render tests obsolete too quickly. These may benefit from prototyping approaches that prioritize speed over test coverage. Similarly, simple scripts or throwaway code rarely justify the TDD investment.
What Project Managers Need to Know About TDD
As a project manager, understanding TDD’s practical implications helps you support your team effectively and set realistic expectations with stakeholders.
Planning and Estimating
TDD often increases initial development time due to the up-front writing of tests. Project managers should factor this into schedules while recognizing it usually reduces time spent on bug fixing and maintenance later.
Velocity Metrics
Traditional velocity measurements may not capture TDD’s value. A feature delivered with comprehensive tests is fundamentally different from one delivered without them, even if both seem functionally complete. Consider measuring quality metrics alongside velocity—defect rates, time spent on bug fixes, and code review efficiency.
Team Training
Teams may require upskilling to effectively adopt TDD—a learning curve is typical, especially for developers new to strict test-first principles.
Code Review Process
TDD changes code reviews. With comprehensive tests, reviewers can focus on design decisions and code clarity rather than manually verifying correctness. Tests serve as executable specifications that reviewers can run, reducing the cognitive burden of reviews and making them faster and more effective.
Quality and Risk Management
With TDD, regression risks are lowered as features evolve. Project managers can have higher confidence in the integrity of incremental changes.
Stakeholder Communication
TDD requires a cultural commitment to quality over speed. Project managers should communicate the long-term benefits clearly, such as reducing late-stage defects and minimizing costly rework.
Integration with Continuous Integration and Continuous Delivery (CI/CD) workflows
TDD works best when integrated with continuous integration and deployment pipelines. Automated test suites run on every code change, providing immediate feedback and preventing broken code from reaching production. Ensure your infrastructure supports this automated testing workflow.
The Importance of TDD in Modern Software Development
Test Driven Development has become a foundational practice in modern software engineering because it drives quality, resilience, and confidence in software products. Its adoption is strongly linked to projects that present low defect rates, faster recovery from production issues, and maintainable codebases well into the future. TDD is more than a testing strategy—it’s a mindset that shapes how successful teams build robust and sustainable software solutions.
Recommended Videos to Help with Software Development
Carefully curated video recommendations for you:
- What are Technical Debt and Refactoring?
- The Software Testing Process: What is User Acceptance Testing – UAT?
- How to Tell if Your Developer is Lying to You – with Duncan McGregor
What Kit does a Project Manager Need?
I asked Project Managers in a couple of forums what material things you need to have, to do your job as a Project Manager. They responded magnificently. I compiled their answers into a Kit list. I added my own.
Check out the Kit a Project Manager needs
Note that the links are affiliated.
Learn Still More
For more great Project Management videos, please subscribe to the OnlinePMCourses YouTube channel.
If you want basic Management Courses – free training hosted on YouTube, with 2 new management lessons a week, check out our sister channel, Management Courses.
For more of our Project Management videos in themed collections, join our Free Academy of Project Management.
For more of our videos in themed collections, join our Free Academy of Project Management.
