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BDD vs TDD vs ATDD : Key Differences

By Jash Unadkat, Technical Content Writer at BrowserStack -

This guidepost aims to describe different testing methods or practices like Behavioral Driven Development (BDD), Test-Driven Development (TDD), Acceptance Test-Driven Development (TDD). It will also help clarify the key differences between these techniques. By the end of this article, one is expected to understand how each method works, key differences, and their particular roles in the development process.

First, let’s start with Test-Driven Development.

What is Test-Driven Development (TDD)?

Test-Driven Development is a testing methodology or a programming practice implemented from a developer’s perspective. In this technique, a QA engineer starts designing and writing test cases for every small functionality of an application. This technique attempts to answer a simple question – Is the code valid? The main intention of this technique is to modify or write a fresh code only when the test fails. Hence it results in lesser duplication of test scripts. This technique is largely popular in agile development ecosystems. In a TDD approach, automated test scripts are written before functional pieces of code. The TDD methodology involves the following steps:

  1. Based on the requirements specified in the documents, a developer writes an automated test case
  2. These tests are executed, and in some cases, they fail as they are developed before the development of an actual feature
  3. The development team then re-factors the code for the test to pass successfully

Re-factoring refers to the process of modifying the code without changing its main functionality or behavior. TDD Process

Benefits of Test-Driven Development:

  • Helps reduce the amount of time required for rework
  • Helps explore bugs or errors very quickly
  • Help get faster feedback
  • Encourages the development of cleaner and better designs
  • Enhances the productivity of the programmer
  • Allows any team member to start working on the code in the absence of a specific team member. This encourages knowledge sharing and collaboration
  • Gives the programmer confidence to change the large architecture of an application easily
  • Results in the creation of extensive code that is flexible and easy to maintain

Tip of the Day: Did you hear about a testing pyramid?

Now, let’s understand everything about Behavioral-Driven Development.

What is Behavioral-Driven Development (BDD)?

Business-Driven Development (BDD) is a testing approach derived from the Test-Driven Development (TDD) methodology. In BDD, tests are mainly based on systems behavior. This approach defines various ways to develop a feature based on its behavior. In most cases, the Given-When-Then approach is used for writing test cases. Let’s take an example for better understanding:

  • Given the user has entered valid login credentials
  • When a user clicks on the login button
  • Then display the successful validation message

As shown above, the behavior is illustrated in a very simple English language, also known as a shared language. This helps everyone in the team responsible for development to understand the feature behavior.

For example, one can try running an easy cross-browser test based on a set of instructions to test across multiple devices as shown in the video.

BDD vs TDD vs ATDD : Key Differences

Try Cross Browser Testing for Free

Key benefits of Behavioral-Driven Development approach:

  • Helps reach a wider audience by the usage of non-technical language
  • Focuses on how the system should behave from the customer’s and the developer’s perspective
  • BDD is a cost-effective technique
  • Reduces efforts needed to verify any post-deployment defects

The image below depicts a typical BDD operation: BDD Process

Image Source: Tutorialspoint

How does BDD help in SDLC?

Debugging the errors in the latter stages of the development life cycle often proves to be very expensive. In the majority of cases, ambiguity in understanding the requirements is the root cause behind this. One needs to ensure that all the development efforts remain aligned towards fulfilling pre-determined requirements. BDD allows developers to do the above by :

  • Allowing the requirements to be defined in a standard approach using simple English
  • Providing several ways to illustrate real-world scenarios for understanding requirements
  • Providing a platform that enables the tech and non-tech teams to collaborate and understand the requirements

Did you know: Cucumber Framework supports Behavior-Driven Development (BDD)

What is Acceptance Test-Driven development?

In Acceptance Test-Driven Development (ATDD) technique, a single acceptance test is written from the user’s perspective. It mainly focuses on satisfying the functional behavior of the system. This technique attempts to answer the question – Is the code working as expected?

Note: Acceptance Test-Driven Development is very similar to Behavioral-Driven Development. However, a key difference between them is: BDD focuses more on the behavior of the feature, whereas ATDD focuses on capturing the accurate requirements.

This technique enhances collaboration among developers, users, and QAs with a common focus on defining the acceptance criteria. The following are some of the key practices in ATDD:

  • Analyzing and discussing the real-world scenarios
  • Deciding the acceptance criteria for those test scenarios
  • Automating the acceptance test cases
  • Focusing on the development of those requirement cases

Want to learn how to create effective test scenarios? Check it out.

Benefits of ATDD

  • Requirements are very clearly analyzed without any ambiguity
  • Encourages collaboration among cross-team members
  • The acceptance test serves as a guide for the entire development process

Key Differences: TDD vs BDD vs ATDD

DefinitionTDD is a development technique that focuses more on the implementation of a featureBDD is a development technique that focuses on the system’s behaviorATDD is a technique similar to BDD focusing more on capturing the requirements
ParticipantsDeveloperDevelopers, Customer, QAsDevelopers, Customers, QAs
Language usedWritten in a language similar to the one used for feature development (Eg. Java, Python, etc)Simple English, (Gherkin) Simple English, Gherkin 
Main FocusUnit TestsUnderstanding RequirementsWriting Acceptance Tests
Tools usedJDave, Cucumber, JBehave, Spec Flow, BeanSpec, Gherkin Concordian, FitNesseGherkin, Dave, Cucumber, JBehave, Spec Flow, BeanSpec, ConcordianTestNG, FitNesse, EasyB, Spectacular, Concordian, Thucydides 

Understanding how these methods work can help developers and other individuals involved in software development, figure out which test strategy works best to serve their purpose. Depending on the kind of project and the results it aims to achieve, the right method (or even a mix of methods) can be deployed to meet specific requirements in the most efficient ways.

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