TDD vs BDD vs ATDD: What’s the Difference? : Aalpha

TDD vs BDD vs ATDD: What’s the Difference

This is a development approach where software requirements are converted into unit test cases before the development of the software. Since it pre-defines the test cases before development it is thus referred to as test-driven design.

Unlike traditionally in software development, where the code is written and then test cases are created and tested, in TDD test cases are first developed before the code is written. The code is then continually tested against the test cases throughout the development process until a complete unit is achieved.

It encourages short development cycles because the test cases are created in the smallest unit of functionality so that each unit is tested and has to pass before other units are added to the design.

There are three rules in TDD that are standard practice namely:

  • The failing test must be written before any production code is written.
  • More of a test should not be written than is sufficient to fail or fail to compile
  • More production code than is sufficient to make the currently failing test pass should not be written

How TDD works

Here is how TDD works:

  • Write a test
  • Run the test or tests and watch them fail
  • Write the code
  • Test the code
  • Refactor
  • Repeat the steps

Benefits of TDD

Some of the benefits of Test-driven development include:

With the tests being specified at the unit level, the developers have knowledge of exactly what they are doing which helps in speeding up development.

Due to clarity, the resultant code is clean, simple, and well-designed.

Because of unit test creation, all the steps of software development are clearly documented.

Because of continually testing each unit the software has fewer bugs overall.

The continuous review of code helps reduces duplication of the code and improves the code organization.

What is Behavior-Driven Development (BDD)?

It is based on the same concept ad Test-Driven Development but goes a step higher. Moreover, it focuses on the functional testing of an application to see the expected behavior.

It is considered an extension of TDD in that it helps to test whether the units are working together.

BDD behavior description: Given, When and Then

In BDD the first step is defining the user story. This is done by gathering all stakeholders who together define it, which in turn forms the acceptance test. Below are definitions of a user story:

Defines a persona.

Defines the wants of a persona.

Define the benefit of including the feature

The team discusses the user story concretely with examples, ideas, and even concepts of the requirements and the expected behavior to capture the concepts in concrete terms that will form the criteria for the acceptance test. Below is the format the acceptance test is created:

This describes the stage of the user to the testing

This is the action the user performs

Describes the expected system outcome.

Benefits of Behavior-Driven development (BDD) approach

There is a clear articulation of the user story which brings clarity on what is being developed and how each user story’s criteria are being met.

The same test can be used over and over to test behavior.

With many stakeholders on board in BDD, a programming language is not used to describe the tests which improve communication because everyone is on the same page.

What is Acceptance Test-Driven Development (ATDD)?

ATDD involves different stakeholders. Plain language is therefore used like in BDD (for everyone to understand) to write acceptance tests based on the user story requirements. However, it’s more like TDD with acceptance tests being written before coding.

The acceptance tests are written based on the external point of view of the user and can be turned into automated acceptance tests.

It has similar benefits to BDD like a common language that improves communication and even shared understanding.

TDD vs BDD vs ATDD: Differences


This is a technique in development that focuses on individual units of a feature that is desired.

This is a technique of development that focuses on the behavior that is expected.

And this is a technique of development that is focused on the needs of the user is met.



Developers, QAs, Customers.

Developers, customers, QAs.

Language used

Written in programming languages.

Gherkin or Simple English

Gherkin/Simple English

Understanding tests

Tests are written by developers for developers

Tests are written for anyone to understand

The test is written for anyone to understand.


Unit tests

Understanding requirements

Writing acceptance tests.


Reduced likelihood and they can be easily tracked down.

Can be more difficult to track down as compared to TDD.

There is more difficulty in tracking them down when you compare to TDD


Projects in that end users are not involved.

The projects driven by user action.

Projects that emphasize on customer experience and with high competition.

Tools used

JDave,Cucumber,JBehave,Spec,Flow,BeanSpec,Gherkin,Concordian,FitNesse,Junit,TestNG,frameworks,Nunit,Selenium tool.

Gherkin, Specflow, Lettuce, Rspec, Cucumber, Concordian, Behat, Mspec, Selenium

Robot, Concordian, EasyB, Spectacular, FIT, Framework, FitNesse


Understanding how each of these methods works goes in a long way in helping developers and other stakeholders know which method will work for them in a particular project. For example, in an e-commerce project, you will find that BDD will be more suitable Or ATDD suitable for an app project, while TDD will be suitable for a project that doesn’t involve end users like servers or APIs.

The three frameworks both ensure that development teams are user-centered and focus on understanding what the user wants and a quality product is developed on time. The user requirements are also captured and tested at high (acceptance tests) and low levels (unit tests) to ensure quality applications are developed. A mix of methods can also be deployed to meet specific requirements efficiently.

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Originally published at on August 26, 2022.



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