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  • Writer's pictureDr. Bohdan Tanyhin

Test-Driven Development

Today, code quality is of paramount importance. Every software product surrounding us consists of a code and ensuring this code is reliable is of the utmost importance. Test-driven development (TDD) can offer a systematic approach and achieve these goals. For example, TDD allows the creation of automated tests before writing code. If tests fail, developers can write code to make them pass. This process enhances development, reduces defects, and fosters a more robust software ecosystem.

In this article, Sencury describes the fundamentals of TDD, its benefits, and practical applications that foster software development with confidence and precision.

What is Test-Driven Development?

TDD stands for a process of software development that uses pre-written test cases to test the software against requirements and ensure it meets all of them. TDD roots come from extreme programming, which aims to boost productivity by organizing people and their working routines. Therefore, all the programming code written is based on test cases – a set of steps to ensure the correct functionality, behavior, features, and quality of an application are being met.

The TDD process focuses on a repetitive short cycle of "red-green-refactor". It is accurately visualized in the picture below.

The TDD process focuses on a repetitive short cycle of "red-green-refactor".

Here, "red" is equal to “fail”, so it marks the test that is intended to fail. "Green" is equal to “pass” and determines the exact quantity of code that should be written to pass the test. “Refactor" is the actual code improvement, but without changing its functionality.

Developer Test-Driven Development

Developer’s test-driven development requires writing a single developer test as well. This test is also called the unit test. Unit tests need little production code written to complete them. The focus of developer TDD lies on every small functionality of the system. It is exactly what TDD is about.

Acceptance Test-Driven Development (ATDD)

Acceptance test-driven development promotes writing only one acceptance test, which will meet software specification requirements. Also, this test can satisfy the behavior of the system. To ensure the test is completed, write the minimum needed production code. As the main idea of ATDD is the focus on the overall behavior of the system, it is also referred to as Behavioral-Driven Development (BDD). Click here to read more about BDD in our corresponding article.

Test-Driven Development Process

Basically, the TDD process is the following:

Writing Tests

It is essential to write a test case that describes the required behavior beforehand the code is produced. This test is supposed to fail due to the code, which does not exist yet.

Running Tests

It is obligatory to execute every test. The one written beforehand has to be executed as well. This test is to fail as there is no functionality that the test describes.

Writing Code

To pass the test, you need to write an essential part of the code. So, the goal is to make the test that previously failed to pass. There is no need to write more code than is needed as this is not the final implementation.

Running Tests

All the tests have to be executed once again. Including the new ones and the previously passed tests. If they all pass, the new code and the code that already exists are working correctly.


When all the tests pass, it is time to refactor the code. It is done without changing the code's behavior but improving structure, readability, and performance. At the same time, functionality stays intact.


The TDD process is repetitive. First, you write the test, then it fails, the next step is to write the code to make it pass, and so on. These iterations are needed to implement all the desired features.

Practical Applications of Test-Driven Development

Being a valuable methodology, TDD is applicable to various software development scenarios. Here are some practical applications of TDD in real-world development:

Web Development

TDD is effective in web development projects. It suits best to ensure web applications function correctly in different browsers and across various devices. The focus of developers is to write tests that simulate user interactions and verify expected behaviors. This way, software experts can catch frontend and backend issues early in development and promote a significantly greater user experience.

API Development

API building can also be enhanced with the help of pre-defined functionality and behavior of the end product. Written tests allow you to cover various use cases, edge cases, scenarios that handle errors, etc. Here, developers can ensure the correct work of APIs in both delivering accurate responses and handling data in the appropriate way.

Legacy Code Refactoring

Legacy codebases can also make use of the TDD approach. Critical functionalities can be tested to see whether there is a need for changes. It is a perfect way to ensure the refactored code meets the expected behavior and has no other flaws. TDD mitigates possible risks of error due to code modifications and acts as a safety net while the code is being refactored.

Agile Development

TDD can work side-by-side and produce positive results with Scrum and Kanban, which belong to Agile methodologies. In Agile, we break tasks into smaller user stories or backlog items to work in iterations. The same idea applies to TDD. Software engineers can test each separate functionality before it is implemented. Therefore, TDD is perfect for iterative and incremental development. With TDD, every sprint ends with the delivery of flawless software.

Open-Source Contributions

Open-source projects can benefit from TDD as well. Making code contributions and writing tests allows software engineers to align changes with project requirements without regression. These tests can substitute documentation as they serve as one. In addition, every code contributor can understand the end-point behavior and collaborate, communicate, or discuss changes based on the documentation provided.

Continuous Integration/Continuous Deployment (CI/CD)

TDD can perfectly integrate with CI/CD pipelines. Automated tests produced during the TDD incorporated into the CI/CD process positively impact frequent code integration, automatic test execution, and quick feedback on the quality of the code. A stable and reliable codebase is not a problem with TDD and CI/CD workflows.

Collaborative Development

Team collaboration is one of the pillars of successful development. Here, TDD can help by defining the expected behavior via tests. Therefore, software engineers will communicate more efficiently until their understanding of software requirements matches. Tests can act as a shared point of reference that impacts collaboration, code reviews, and knowledge sharing within a team.

Why Do You Need Test-Driven Development?

Many organizations ask themselves whether there is a potential need for TDD. It depends on the organization itself, its basic needs, and its capabilities. With TDD any business will:

  • be able to deliver continuously and innovate faster with the robust code

  • achieve extensible and flexible code with the ability to refactor or move it

  • receive tests that were also tested by a development team that verifies test failure

  • obtain an easily testable code

  • have an effortless implementation of requirements with the written function

Test-Driven Development at Sencury

Sencury offers our QA strategy consulting service as a starting point to decide on the need for the TDD and its extent. Also, QA strategy consulting exists for designing a proper balance between manual and automatic testing. It is of great benefit as there are many other complex methodological decisions to make. For instance,

  • cooperation between QA and the development team (particularly, sanity testing and regression testing),

  • cooperation between QA and BA,

  • planning of QA team mobilization for different phases such as the test documentation phase, dev process support by QA, UAT, production support phase, and change request implementation phase.

Naturally, Sencury offers manual and QA automation testing teams. The latter amends a unit test that developers write. Both constitute crucial elements of TDD.


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