TDD vs BDD vs ATDD : Key Differences

In software development and testing, it is important to know and be able to distinguish between Test Driven Development (TDD), Behaviour Driven Development (BDD), and Acceptance Test Driven Development (ATDD) to yield change in the approach of testing and collaboration among clients and developers. TDD is primarily centered on writing tests first before writing the actual codes, BDD is in the same way focused on the behaviors where test cases are designed and lastly, ATDD is where all the stakeholders, practitioners, customers, and end users are involved in acceptance criteria. These methodologies have quite different approaches and focusing on the correct occasions to apply them can help the ‘right’ software to be developed more efficiently, effectively, and with more consideration for the client.

What is Test-Driven Development (TDD)?

Test-Driven Development (TDD) is an approach in software development that involves designing and implementing codes based on written tests. It implements a cycle of a written failing test that prescribes a specific function or an improvement, writing the least amount of code possible to make the test pass, and then refactoring the code and keeping the test passing. TDD, as it is well known, focuses on the refactoring of code into small change iterations with all the new features being tested. It is useful to catch bugs early to help remember the use cases and to come up with a cleaner design.

Key features of TDD:

• Test-First Approach: This is created before the coding that will provide the implementation for it.
• Red-Green-Refactor Cycle: The process is based on the following three steps: Write a test that fails (Red), Write the code and make the test pass (Green), and finally optimize the code while the test is still passing (Refactor).
• Small Iterations: It evolves step by step where each test is the smallest possible useful part of the application.
• Continuous Feedback: Testing is done after each modification so that one can observe how the code behaves, providing the end of each testing.
• Improved Code Quality: Mainly, TDD is based on testing from the beginning, which leads to cleaner and more maintainable code significantly reducing the number of bugs.

What is Behaviour-Driven Development (BDD)?

Behaviour-driven development (BDD) is an approach to agile methodologies that goes a step further than test-driven development (TDD) and involves not only technical people like developers and testers but also business people like analysts. It is concentrated on building consensus about the expected interaction with the system and providing precise documentation for that in the form of scenarios. Such scenarios are usually documented using templates like the ‘Given-When-Then’ format which defines the state, event and expected result of that feature. BDD seeks to bring together software developers and testers by ensuring that even those who do not code have a clear understanding of what the software is supposed to do, thus improving the software development and testing workflows.

Key features of BDD:

• Collaborative Approach: It does not differ from any other methodology where the major stakeholders, the developers, testers, and the business representatives are involved in defining the requirements.
• Scenarios in Plain Language: Leverages first-person narrative (also known as “given-when-then” format) to explain system behaviour.
• Focus on Behaviour: Stresses more on defining the behaviour of the application that needs to be developed rather than laying down the methodology of developing it.
• Executable Specifications: The best part of scenarios is that these can be transformed into truly automated tests that allow for checking the correct behaviour of the software.
• Improved Communication: Improves collaboration between those still deep in the technical work and those more focused on the creative end and business strategy, by minimizing confusion and capturing everyone’s vision for the project.

What is Acceptance Test-Driven Development (ATDD)?

ATDD stands for Acceptance Test Driven Development is a development approach in which the development, testing and business stakeholders work together in development during the definition of the acceptance characteristics of a feature. These criteria are written as acceptance tests which are the description of how the system should work from the user perspective. These tests were confirming a contract between all the members about the developed feature and that the feature met the specific requirements that all parties agreed on. Compared to traditional approaches, ATDD helps to start and sustain communication with stakeholders as early as possible to avoid misinterpretation and guarantee the business value of the developed result. It incorporates testing into the development cycle so that the team can be assured that the software meets some set criteria at any given time in the process of its development.

Key features of ATDD:

• Acceptance Criteria: These are based on user-specified acceptance criteria and emphasize what the system should be able to do for business requirements.
• User-Centric Approach: Stress the end user’s view of what constitutes an asset to be included and incorporated into the software.
• Collaborative Process: Reduced to a process that employs the cooperation of both the development team and the business stakeholders in choosing.
• Automated Testing: Acceptance tests are usually carried out automatically since they can be performed at several stages of development.
• Alignment with Business Goals: Guarantees that the developed software meets the business needs as all the requirements are checked to ensure that a feature was developed.

TDD vs BDD vs ATDD

Test-Driven Development (TDD) Applications

• Library and API Development: Verifies that the code in the background functions or various classes executes properly.
• Algorithm Implementation: Assists in checking the validity of algorithms especially when computations are intensified or data analysis and manipulation are involved.
• Refactoring Legacy Code: This helps in refactoring the old large code bases as it ensures that the safety of the code is not compromised during the process.
• Developing Microservices: Guarantees the correctness of microservices with an emphasis on units.
• Continuous Integration Pipelines: Helps include automated tests in CI and make sure that each build contains a set of tests that will pass all the time.

Behaviour-Driven Development (BDD) Applications

• Feature Development in Agile Projects: Ensures there is a correlation with business needs which guarantees that enhancements work as anticipated.
• Cross-functional collaboration: Cultivates the working relationship between developers, testers, and the business side when it comes to defining what is required.
• Web Application Development: Verifies that an actual usage of a web application is correct through testing of scenarios the user might experience.
• Acceptance Testing for Complex Systems: Coupled with acceptance tests for systems having many user stories or even interactions.
• Documentation of Business Rules: It acts as a current living document that depicts how the system should perform which can be understood by the non–IT oriented individuals.

Acceptance Test-Driven Development (ATDD) Applications

• Requirement Validation in Enterprise Systems: The primary focus is to ensure that the enterprise applications are operational with business stakeholders’ specific acceptance standards set.
• Regulatory Compliance Software: The following process confirms that the software is fully compliant with rigorous regulatory standards through acceptance tests that are already defined.
• Agile Development in Regulated Industries: Make certain that every aspect being developed fulfils the purpose of the business and is in line with legal requirements.
• User-Centric Product Development: Concentrates on providing the customers’ demands on specific products and services, which results in a greater level of satisfaction.
• Continuous Delivery: Helps deploy continuous delivery by establishing the assurance that every feature is subjected to the acceptance tests before deployment.

Conclusion

In conclusion, TDD, BDD, and ATDD are similar but different development methodologies that in their totality provide definite value to the SD process. TDD aims at writing unit tests for the source code to ensure it is correct, BDD aims at matching the behaviours with the users’ expectations through the scenario tests, and ATDD focuses on testing features based on business-accepting criteria. Both complement each other and help facilitate collaboration, strengthen the code, and guarantee that the result matches the technical and commercial objectives when incorporated into today’s agile environments.