Test-Driven Development In A Nutshell

As the name suggests, TDD is a test-driven technique for delivering high-quality software rapidly and sustainably. It is an iterative approach based on the idea that a failing test should be written before any code for a feature or function is written. Test-Driven Development (TDD) is an approach to software development that relies on very short development cycles.

Concept OverviewTest-Driven Development (TDD) is a software development methodology that emphasizes writing tests before writing code. It follows a cycle of red-green-refactor, where developers first write failing tests (red), then write the minimum code to make the tests pass (green), and finally refactor the code for simplicity and maintainability. TDD aims to improve code quality, reduce defects, and enhance the development process’s efficiency.
Key PrinciplesTDD is guided by several key principles:
1. Test First: Write test cases before writing any code to specify the desired behavior.
2. Incremental Development: Develop code in small, manageable increments, one test case at a time.
3. Simplicity: Keep the code as simple as possible to meet the test case requirements.
4. Continuous Testing: Run tests frequently to catch defects early in the development process.
5. Refactoring: Improve the code’s design and structure while maintaining test coverage.
TDD CycleThe TDD cycle consists of the following steps:
1. Red: Write a failing test case that describes the desired functionality. This test initially fails because the code doesn’t exist.
2. Green: Write the minimum code necessary to make the test case pass. This involves implementing the required functionality.
3. Refactor: Refactor the code to improve its design, readability, and maintainability while ensuring the test cases still pass.
BenefitsImplementing TDD offers several benefits:
1. Improved Code Quality: Frequent testing reduces the likelihood of defects and bugs.
2. Early Detection of Issues: Defects are identified and fixed at an early stage, reducing debugging time.
3. Design Clarity: TDD encourages clean and modular code design.
4. Better Documentation: Test cases serve as documentation of expected behavior.
5. Enhanced Collaboration: Tests provide a common understanding between developers and stakeholders.
Challenges and RisksChallenges in adopting TDD include a potential learning curve, the need for a mindset shift towards testing, and the time investment required to write and maintain tests. Some argue that TDD can lead to an excessive focus on testing over other essential aspects of software development.
ApplicationsTDD is commonly applied in software development, particularly in areas where code quality, reliability, and maintainability are critical. It is used in various domains, including web development, mobile app development, and embedded systems development.
Tools and FrameworksVarious testing frameworks and tools support TDD in different programming languages. Examples include JUnit and TestNG for Java, RSpec for Ruby, and pytest for Python. Behavior-Driven Development (BDD) frameworks like Cucumber are also used for TDD.

Understanding Test-Driven Development

Test-Driven Development has had a significant influence on software design, with a particular focus on non-functional requirements such as usability, security, and maintainability.

These small tests allow developers to design systems from scratch, adding value rapidly and increasing confidence in the system itself.

A typical Test-Driven Development cycle

TDD invariably follows the “Red-Green-Refactor” cycle, described as follows:

  • Start by adding a test unit to the test suite. This test unit should describe an aspect of the program. 
  • (Red) Run all tests, which should fail because the program lacks that feature.
  • (Green) Write just enough code in the simplest way possible to enable the test to pass. This step is sometimes called “make it pass”.
  • Run all tests once again.
  • (Refactor) Enhance the original code while keeping tests green. Ensure that a focus on simplicity is maintained.
  • Repeat and accumulate unit tests over time.

Strengths and weaknesses of TDD


Increased code quality resulting from the reduction in defects and errors

TDD forces developers to consider the purpose and specification of code.

It also helps developers simplify code writing and avoid complex code that can harbor bugs.

Lastly, TDD refactoring ensures that code changes or new code do not impact the integrity of the existing code.

Reduction in batch size

In other agile methodologies, developers work on a feature until completion with little input from others.

TDD encourages the developer to reduce the batch size to improve project visibility, flexibility, and stakeholder collaboration.

Ultimately, this also makes TDD a customer-centric agile process.

Encourages high developer morale

On occasion, developers become demoralized in the face of large and complex projects.

TDD distills large projects into many smaller pieces that deliver quick and relatively easy wins for the developer.

In addition to improving morale and confidence, the developer knows what has been completed and what work remains to be completed.


May take more time to implement initially

Programmers who have become accustomed to writing code that can be run immediately may find TDD slow and difficult to implement.

The same can be said for programmers who have never written tests in the first place.

However, any perceived slowness is an illusion at best.

Although TDD may take some getting used to, it does deliver significant benefits to efficiency as development progresses.

Poorly maintained or abandoned test suites

A lack of test suite maintenance can lead to a TDD cycle with a prohibitively long running time.

Test suites may be also be abandoned or seldom run because of poor maintenance or changes to team composition.

Test-driven development example

In the following test-driven development example, consider a user management system enabling new customers to create a username and password for future authentication.

For the username and password to be valid, certain business rules should be followed.

To analyze multiple rules would be beyond the scope of this article, so for the sake of brevity, we will describe one rule that validates the minimum length of the password.

Let’s also assume that the company is stringent on security and requires the password to be at least 12 characters.

With this rule defined, we can now create our tests and code accordingly using a language such as Java or Python.

Step 1 – Write a failing test case

The development team starts by writing the code for a failing test case. In this example, they assert that if the length of a password entered by the user is 7 characters, then they should receive an error message.

This can simply read as follows: “Length of password must be at least 12 characters.

To achieve this, the team calls a function “ValidatePassword” which takes a string argument.

The function also becomes part of a class called “ValidatorService” which is initiated in the setUp function of the test class.

Step 2 – Run the unit test

The team then runs the test but receives an error because it has not yet created the “ValidatorService” class.

The class is created and the test is run once more.

Remember that test-driven development requires that the team write just enough code so that the failing test passes.

After running the test for a second time, another error related to the test looking for the function presents itself.

The team develops a placeholder function and runs the test for the third time.

The test passes.

Step 3 – Create the code

Now it’s time to write the code for the actual functionality of the user management system.

In other words, to authenticate the length of the password and execute the test case.

The team runs a few generic test cases and each passes, but they notice as a result that there is repetition in the code.

They decide to refactor the code to maintain a focus on simplicity without impacting the viability of the test.

Since the team is using PHPUnit to write the code, they can take advantage of the “dataprovider” feature which makes the refactoring process simpler.

The team also refactors the implementation code, ensuring that after every change the test cases still pass.

At this point, more test cases can be added to validate different business rules. 

The password, for example, may require a certain number of special characters or upper case letters.

Whatever the rules that are implemented, it’s important that developers refactor the code as and when required so that problems which cause failed tests can be pinpointed with ease.


Acceptance Test-Driven Development (ATDD) is a part of the agile methodology where automated tests are written from the user’s perspective. Unlike test-driven development – where acceptance tests are created from the perspective of the developer – ATDD advocates the automation of tests from the various perspectives of the user.

Whereas a test-driven development favors rapid delivery in short cycles by creating test units.

An acceptance ted-driven development approach, also part of the agile methodology, tries to balance the test with a user’s perspective in mind.

More precisely, it does that by evaluating and incorporating in the testing environment collaboration between what are known as the “three amigos” (customer, developer, and tester).

Key takeaways

  • Test-Driven Development is an agile software development approach that favors the rapid delivery of very short development cycles.
  • Fundamental to Test-Driven Development is the “Red-Green-Refactor” test cycle. TDD argues that fail tests should be conducted before any feature or function code is written.
  • Test-Driven Development increases code quality and developer morale while reducing batch sizes. However, some project teams may experience a steep initial learning curve – particularly if they are unaccustomed to the methodology.

Key Highlights

  • Definition and Approach:
    • TDD is a test-driven technique for delivering high-quality software rapidly and sustainably.
    • It’s an iterative approach where failing tests are written before any code for a feature is developed.
  • TDD Cycle:
    • TDD follows the “Red-Green-Refactor” cycle:
      • Red: Write a failing test for the desired functionality.
      • Green: Write the simplest code to make the test pass.
      • Refactor: Enhance the code while keeping the tests passing.
    • This cycle helps maintain code integrity and simplifies development.
  • Influence on Software Design:
    • TDD emphasizes non-functional requirements like usability, security, and maintainability.
    • It allows developers to design systems incrementally and confidently.
  • Strengths of TDD:
    • Increased code quality through reduced defects and improved specification.
    • Forces developers to consider code purpose and specification.
    • Encourages simple code design, avoiding complex and buggy code.
    • Supports code refactoring without compromising existing functionality.
    • Reduces batch size, improving project visibility and stakeholder collaboration.
    • Boosts developer morale with quick wins and clearer project progress.
  • Weaknesses of TDD:
    • Initial implementation might take more time for those new to TDD.
    • Poorly maintained test suites can lead to slow cycles or abandonment.
  • TDD Example:
    • Example of implementing a password length validation rule using TDD.
    • Steps include writing failing tests, creating code to pass the tests, and refactoring.
  • TDD vs. ATDD:
    • TDD focuses on writing tests from the developer’s perspective.
    • Acceptance Test-Driven Development (ATDD) focuses on writing tests from the user’s perspective.
    • ATDD aims for collaboration between customers, developers, and testers.
  • Key Takeaways:
    • TDD is an agile approach emphasizing short development cycles and high-quality code.
    • TDD follows a cycle of writing failing tests, implementing code, and refactoring.
    • TDD improves code quality, developer morale, and project visibility.
    • Initial learning curve might be challenging for teams new to TDD.

Connected Agile & Lean Frameworks


AIOps is the application of artificial intelligence to IT operations. It has become particularly useful for modern IT management in hybridized, distributed, and dynamic environments. AIOps has become a key operational component of modern digital-based organizations, built around software and algorithms.


AgileSHIFT is a framework that prepares individuals for transformational change by creating a culture of agility.

Agile Methodology

Agile started as a lightweight development method compared to heavyweight software development, which is the core paradigm of the previous decades of software development. By 2001 the Manifesto for Agile Software Development was born as a set of principles that defined the new paradigm for software development as a continuous iteration. This would also influence the way of doing business.

Agile Program Management

Agile Program Management is a means of managing, planning, and coordinating interrelated work in such a way that value delivery is emphasized for all key stakeholders. Agile Program Management (AgilePgM) is a disciplined yet flexible agile approach to managing transformational change within an organization.

Agile Project Management

Agile project management (APM) is a strategy that breaks large projects into smaller, more manageable tasks. In the APM methodology, each project is completed in small sections – often referred to as iterations. Each iteration is completed according to its project life cycle, beginning with the initial design and progressing to testing and then quality assurance.

Agile Modeling

Agile Modeling (AM) is a methodology for modeling and documenting software-based systems. Agile Modeling is critical to the rapid and continuous delivery of software. It is a collection of values, principles, and practices that guide effective, lightweight software modeling.

Agile Business Analysis

Agile Business Analysis (AgileBA) is certification in the form of guidance and training for business analysts seeking to work in agile environments. To support this shift, AgileBA also helps the business analyst relate Agile projects to a wider organizational mission or strategy. To ensure that analysts have the necessary skills and expertise, AgileBA certification was developed.

Agile Leadership

Agile leadership is the embodiment of agile manifesto principles by a manager or management team. Agile leadership impacts two important levels of a business. The structural level defines the roles, responsibilities, and key performance indicators. The behavioral level describes the actions leaders exhibit to others based on agile principles. 

Andon System

The andon system alerts managerial, maintenance, or other staff of a production process problem. The alert itself can be activated manually with a button or pull cord, but it can also be activated automatically by production equipment. Most Andon boards utilize three colored lights similar to a traffic signal: green (no errors), yellow or amber (problem identified, or quality check needed), and red (production stopped due to unidentified issue).

Bimodal Portfolio Management

Bimodal Portfolio Management (BimodalPfM) helps an organization manage both agile and traditional portfolios concurrently. Bimodal Portfolio Management – sometimes referred to as bimodal development – was coined by research and advisory company Gartner. The firm argued that many agile organizations still needed to run some aspects of their operations using traditional delivery models.

Business Innovation Matrix

Business innovation is about creating new opportunities for an organization to reinvent its core offerings, revenue streams, and enhance the value proposition for existing or new customers, thus renewing its whole business model. Business innovation springs by understanding the structure of the market, thus adapting or anticipating those changes.

Business Model Innovation

Business model innovation is about increasing the success of an organization with existing products and technologies by crafting a compelling value proposition able to propel a new business model to scale up customers and create a lasting competitive advantage. And it all starts by mastering the key customers.

Constructive Disruption

A consumer brand company like Procter & Gamble (P&G) defines “Constructive Disruption” as: a willingness to change, adapt, and create new trends and technologies that will shape our industry for the future. According to P&G, it moves around four pillars: lean innovation, brand building, supply chain, and digitalization & data analytics.

Continuous Innovation

That is a process that requires a continuous feedback loop to develop a valuable product and build a viable business model. Continuous innovation is a mindset where products and services are designed and delivered to tune them around the customers’ problem and not the technical solution of its founders.

Design Sprint

A design sprint is a proven five-day process where critical business questions are answered through speedy design and prototyping, focusing on the end-user. A design sprint starts with a weekly challenge that should finish with a prototype, test at the end, and therefore a lesson learned to be iterated.

Design Thinking

Tim Brown, Executive Chair of IDEO, defined design thinking as “a human-centered approach to innovation that draws from the designer’s toolkit to integrate the needs of people, the possibilities of technology, and the requirements for business success.” Therefore, desirability, feasibility, and viability are balanced to solve critical problems.


DevOps refers to a series of practices performed to perform automated software development processes. It is a conjugation of the term “development” and “operations” to emphasize how functions integrate across IT teams. DevOps strategies promote seamless building, testing, and deployment of products. It aims to bridge a gap between development and operations teams to streamline the development altogether.

Dual Track Agile

Product discovery is a critical part of agile methodologies, as its aim is to ensure that products customers love are built. Product discovery involves learning through a raft of methods, including design thinking, lean start-up, and A/B testing to name a few. Dual Track Agile is an agile methodology containing two separate tracks: the “discovery” track and the “delivery” track.

eXtreme Programming

eXtreme Programming was developed in the late 1990s by Ken Beck, Ron Jeffries, and Ward Cunningham. During this time, the trio was working on the Chrysler Comprehensive Compensation System (C3) to help manage the company payroll system. eXtreme Programming (XP) is a software development methodology. It is designed to improve software quality and the ability of software to adapt to changing customer needs.

Feature-Driven Development

Feature-Driven Development is a pragmatic software process that is client and architecture-centric. Feature-Driven Development (FDD) is an agile software development model that organizes workflow according to which features need to be developed next.

Gemba Walk

A Gemba Walk is a fundamental component of lean management. It describes the personal observation of work to learn more about it. Gemba is a Japanese word that loosely translates as “the real place”, or in business, “the place where value is created”. The Gemba Walk as a concept was created by Taiichi Ohno, the father of the Toyota Production System of lean manufacturing. Ohno wanted to encourage management executives to leave their offices and see where the real work happened. This, he hoped, would build relationships between employees with vastly different skillsets and build trust.

GIST Planning

GIST Planning is a relatively easy and lightweight agile approach to product planning that favors autonomous working. GIST Planning is a lean and agile methodology that was created by former Google product manager Itamar Gilad. GIST Planning seeks to address this situation by creating lightweight plans that are responsive and adaptable to change. GIST Planning also improves team velocity, autonomy, and alignment by reducing the pervasive influence of management. It consists of four blocks: goals, ideas, step-projects, and tasks.

ICE Scoring

The ICE Scoring Model is an agile methodology that prioritizes features using data according to three components: impact, confidence, and ease of implementation. The ICE Scoring Model was initially created by author and growth expert Sean Ellis to help companies expand. Today, the model is broadly used to prioritize projects, features, initiatives, and rollouts. It is ideally suited for early-stage product development where there is a continuous flow of ideas and momentum must be maintained.

Innovation Funnel

An innovation funnel is a tool or process ensuring only the best ideas are executed. In a metaphorical sense, the funnel screens innovative ideas for viability so that only the best products, processes, or business models are launched to the market. An innovation funnel provides a framework for the screening and testing of innovative ideas for viability.

Innovation Matrix

According to how well defined is the problem and how well defined the domain, we have four main types of innovations: basic research (problem and domain or not well defined); breakthrough innovation (domain is not well defined, the problem is well defined); sustaining innovation (both problem and domain are well defined); and disruptive innovation (domain is well defined, the problem is not well defined).

Innovation Theory

The innovation loop is a methodology/framework derived from the Bell Labs, which produced innovation at scale throughout the 20th century. They learned how to leverage a hybrid innovation management model based on science, invention, engineering, and manufacturing at scale. By leveraging individual genius, creativity, and small/large groups.

Lean vs. Agile

The Agile methodology has been primarily thought of for software development (and other business disciplines have also adopted it). Lean thinking is a process improvement technique where teams prioritize the value streams to improve it continuously. Both methodologies look at the customer as the key driver to improvement and waste reduction. Both methodologies look at improvement as something continuous.

Lean Startup

A startup company is a high-tech business that tries to build a scalable business model in tech-driven industries. A startup company usually follows a lean methodology, where continuous innovation, driven by built-in viral loops is the rule. Thus, driving growth and building network effects as a consequence of this strategy.

Minimum Viable Product

As pointed out by Eric Ries, a minimum viable product is that version of a new product which allows a team to collect the maximum amount of validated learning about customers with the least effort through a cycle of build, measure, learn; that is the foundation of the lean startup methodology.

Leaner MVP

A leaner MVP is the evolution of the MPV approach. Where the market risk is validated before anything else


Kanban is a lean manufacturing framework first developed by Toyota in the late 1940s. The Kanban framework is a means of visualizing work as it moves through identifying potential bottlenecks. It does that through a process called just-in-time (JIT) manufacturing to optimize engineering processes, speed up manufacturing products, and improve the go-to-market strategy.


Jidoka was first used in 1896 by Sakichi Toyoda, who invented a textile loom that would stop automatically when it encountered a defective thread. Jidoka is a Japanese term used in lean manufacturing. The term describes a scenario where machines cease operating without human intervention when a problem or defect is discovered.

PDCA Cycle

The PDCA (Plan-Do-Check-Act) cycle was first proposed by American physicist and engineer Walter A. Shewhart in the 1920s. The PDCA cycle is a continuous process and product improvement method and an essential component of the lean manufacturing philosophy.

Rational Unified Process

Rational unified process (RUP) is an agile software development methodology that breaks the project life cycle down into four distinct phases.

Rapid Application Development

RAD was first introduced by author and consultant James Martin in 1991. Martin recognized and then took advantage of the endless malleability of software in designing development models. Rapid Application Development (RAD) is a methodology focusing on delivering rapidly through continuous feedback and frequent iterations.

Retrospective Analysis

Retrospective analyses are held after a project to determine what worked well and what did not. They are also conducted at the end of an iteration in Agile project management. Agile practitioners call these meetings retrospectives or retros. They are an effective way to check the pulse of a project team, reflect on the work performed to date, and reach a consensus on how to tackle the next sprint cycle. These are the five stages of a retrospective analysis for effective Agile project management: set the stage, gather the data, generate insights, decide on the next steps, and close the retrospective.

Scaled Agile

Scaled Agile Lean Development (ScALeD) helps businesses discover a balanced approach to agile transition and scaling questions. The ScALed approach helps businesses successfully respond to change. Inspired by a combination of lean and agile values, ScALed is practitioner-based and can be completed through various agile frameworks and practices.


The SMED (single minute exchange of die) method is a lean production framework to reduce waste and increase production efficiency. The SMED method is a framework for reducing the time associated with completing an equipment changeover.

Spotify Model

The Spotify Model is an autonomous approach to scaling agile, focusing on culture communication, accountability, and quality. The Spotify model was first recognized in 2012 after Henrik Kniberg, and Anders Ivarsson released a white paper detailing how streaming company Spotify approached agility. Therefore, the Spotify model represents an evolution of agile.

Test-Driven Development

As the name suggests, TDD is a test-driven technique for delivering high-quality software rapidly and sustainably. It is an iterative approach based on the idea that a failing test should be written before any code for a feature or function is written. Test-Driven Development (TDD) is an approach to software development that relies on very short development cycles.


Timeboxing is a simple yet powerful time-management technique for improving productivity. Timeboxing describes the process of proactively scheduling a block of time to spend on a task in the future. It was first described by author James Martin in a book about agile software development.


Scrum is a methodology co-created by Ken Schwaber and Jeff Sutherland for effective team collaboration on complex products. Scrum was primarily thought for software development projects to deliver new software capability every 2-4 weeks. It is a sub-group of agile also used in project management to improve startups’ productivity.


Scrumban is a project management framework that is a hybrid of two popular agile methodologies: Scrum and Kanban. Scrumban is a popular approach to helping businesses focus on the right strategic tasks while simultaneously strengthening their processes.

Scrum Anti-Patterns

Scrum anti-patterns describe any attractive, easy-to-implement solution that ultimately makes a problem worse. Therefore, these are the practice not to follow to prevent issues from emerging. Some classic examples of scrum anti-patterns comprise absent product owners, pre-assigned tickets (making individuals work in isolation), and discounting retrospectives (where review meetings are not useful to really make improvements).

Scrum At Scale

Scrum at Scale (Scrum@Scale) is a framework that Scrum teams use to address complex problems and deliver high-value products. Scrum at Scale was created through a joint venture between the Scrum Alliance and Scrum Inc. The joint venture was overseen by Jeff Sutherland, a co-creator of Scrum and one of the principal authors of the Agile Manifesto.

Six Sigma

Six Sigma is a data-driven approach and methodology for eliminating errors or defects in a product, service, or process. Six Sigma was developed by Motorola as a management approach based on quality fundamentals in the early 1980s. A decade later, it was popularized by General Electric who estimated that the methodology saved them $12 billion in the first five years of operation.

Stretch Objectives

Stretch objectives describe any task an agile team plans to complete without expressly committing to do so. Teams incorporate stretch objectives during a Sprint or Program Increment (PI) as part of Scaled Agile. They are used when the agile team is unsure of its capacity to attain an objective. Therefore, stretch objectives are instead outcomes that, while extremely desirable, are not the difference between the success or failure of each sprint.

Toyota Production System

The Toyota Production System (TPS) is an early form of lean manufacturing created by auto-manufacturer Toyota. Created by the Toyota Motor Corporation in the 1940s and 50s, the Toyota Production System seeks to manufacture vehicles ordered by customers most quickly and efficiently possible.

Total Quality Management

The Total Quality Management (TQM) framework is a technique based on the premise that employees continuously work on their ability to provide value to customers. Importantly, the word “total” means that all employees are involved in the process – regardless of whether they work in development, production, or fulfillment.


The waterfall model was first described by Herbert D. Benington in 1956 during a presentation about the software used in radar imaging during the Cold War. Since there were no knowledge-based, creative software development strategies at the time, the waterfall method became standard practice. The waterfall model is a linear and sequential project management framework. 

Read Also: Continuous InnovationAgile MethodologyLean StartupBusiness Model InnovationProject Management.

Read Next: Agile Methodology, Lean Methodology, Agile Project Management, Scrum, Kanban, Six Sigma.

Main Guides:

Main Case Studies:

About The Author

Scroll to Top