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TDD vs BDD vs ATDD: Key Differences

October 17, 2023Tejas Adesara
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BDD vs TDD vs ATDD: Key Differences
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Writing code is only one component of the software development process. One of the most challenging difficulties for developers is thoroughly testing their code to verify it meets the essential criteria and standards. This is where testing methodologies such as Test Driven Development (TDD) and Behavioral Driven Development (BDD) can help. TDD is a method that involves writing tests before developing code, whereas BDD focuses on defining a system’s behavior through testing. TDD vs BDD vs ATDD, all these strategies are commonly used and can assist developers in overcoming the challenges of forecasting user requirements and developing simple tests. Furthermore, Acceptance Test-Driven Development (ATDD) is a prominent testing practice that may be used to guarantee that the code fulfills the end user’s expectations.

Testing practices are essential for software development. They involve writing tests and time planning to ensure the development teams understand user requirements and develop quality software products. They are also used for automated test analysis. This blog will explore the usefulness of these testing practices and help you decide which strategy to use in your software development process.

Table Of Contents

What is Test Driven Development (TDD)?

Test-Driven Development (TDD) is a testing practice that develops the test case before the developers initiate writing the code. The corresponding test cases are small units according to the specified requirement of the software. 

TDD focuses on feature implementation of unit tests. It depends on the iteration of a short development cycle to transform requirements into explicit test cases. The intention of writing the code is to pass the test. Subsequently, the code is restructured and enhanced to guarantee high code quality and exclude any technical deficits. The corresponding cycle in TDD that continuously tests the written code is referred to as the Red-Green-Ref. The ‘Red’, ‘Green’ and ‘Refactor’ phases iterate for each new feature either added or updated.

It is best to implement a TDD framework when there is a definite set of inputs with predictable outputs. Specifically, when the logic adopted to obtain those outputs is complex to implement. TDD approach helps streamline the complexity. It allows developers to disintegrate huge problems into tiny chunks and concentrate on one aspect at a time.

The test-first approach of TDD helps alleviate the crucial bottlenecks that impede the software delivery process and quality. TDD facilitates continuous feedback, bug fixes, and implementation of new features. Consequently, it ensures that the software development process works as intended.

TDD improves the collaboration between the QA teams, the development teams, and the client. It facilitates the creation of tests upfront. So, the teams don’t have to waste time developing the test scripts again.

One of the central concepts that TDD adopts is to “get something working now and perfect it later” Once each test completes, the code is restructured. Subsequently, a similar test is executed again. The process repeats until each test unit works as per the expected specifications.

Benefits of TDD

i. Ensures accurate tests and flexible codebase

TDD approach leads to accurate test results. Regardless of the code being implemented, TDD aims to pass the test if the business logic is robust. If any of the tests fail, TDD instantly detects the code change and informs the developers to focus on maintaining the test accuracy. It avoids the adverse effect of one unit test’s failure on another. Hence, it always ensures accurate tests. The improved test accuracy leads to the creation of a codebase that is easy to maintain and flexible. Ultimately, it reinforces the programmer’s confidence and eliminates the fear of code changes.

ii. Fosters the development of optimized code:

TDD enables developers to effectively analyze the client’s requirements and demand clarity when they are not properly defined. The precise requirements as input will lead to the creation of optimized code.

iii. Simplifies testing of new functionalities:

The test coverage of TDD is quite higher than the traditional development models. The reason is TDD emphasizes developing tests for each of the functionalities in advance. So, the addition and testing of newly implemented functionalities become quite easier in all the stages of development. One of the significant differences between TDD vs BDD is that, unlike BDD, TDD makes it easier to test the newly added functionalities.

iv. Simplifies code refactoring

This testing method makes refactoring more convenient because it allows you to access your code and modify it. If the test fails, you get instant feedback on what errors occurred.

v. Streamlines writing documentation:

TDD allows developers to write tests for validating micro-level functionalities. Hence, it simplifies the process of writing documentation.

Process of TDD

The standard TDD process follows the following three stages:

Stage 1: Discovery:

The TDD process commences with a new user story. This stage involves exploring and discussing the user story. Its outcome determines the system’s agreed behavior. Usually, the team members possessing specific business domain proficiency declare the projected behavior within a feature file. They will share that file with the development teams.

Stage 2: Formulation:

In this stage, test examples are generated, discussed, decided, and approved. Subsequently, the models are documented so that they can automate testing and development processes. The outcome of this stage represents the documented examples that can be used as acceptance tests in the future.  The developers now write code that executes those predictable behaviors. Moreover, they follow up the test code which they will use to validate that behavior against the proposed business logic. The purpose behind this is to make sure that it fulfils the client’s requirements.

Stage 3: Automation:

In this phase, all the documented examples are implemented as per the determined system behavior. Subsequently, an automation BDD test is created for every user story to supervise the development process. So, the outcomes of this stage represent code execution and automation tests.

In the next step, the testers assess the application. They accomplish the same by validating those tests against the estimated behavior mentioned in feature files. Finally, the developers create the BDD code.

Pros and Cons of Test Driven Development (TDD)

Pros of Test Driven DevelopmentCons of Test Driven Development
1. You only have to write the necessary code
2. Easy to maintain and refactor
3. Enables writing detailed documentation
4. Allows adding and testing new functionalities
5. High test accuracy
6. High test coverage
7. Saves time because it needs less debugging
8. Facilitates collaboration on team members’ code
1. Developers require more time to understand the interface and write test codes
2. Tests must be maintained when requirements alter
3. Demands the involvement of the entire team
4. Complex to learn

What is Behavioral Driven Development (BDD)?

Behavioral Driven Development (BDD) is a development technique that focuses on the way an application must behave from the user’s perspective. Simply put, the corresponding tests are based on the expected system behavior.

Alternatively, it is defined as a testing approach that instigates collaboration between all teams working on a project’s delivery. It defines and validates a system’s behavior in a language that is easily understood by all involved teams.  This definition is used as a seed for a TDD-centered process.

As we can notice, one of the important differences between TDD vs BDD is that BDD is based on the anticipated system’s behavior whereas TDD is based on the implementation of features of unit tests. Instead of testing the code’s implementation, BDD aims to validate behaviors and scenarios.

A BDD test approach is expected to provide full test coverage wherein the behavioral tests use a common language to comprehensively illustrate the system’s behavior to all teams. Since the test cases are written in simple English, the BDD test approach eliminates the gap between the non-technical and technical teams.

Key Benefits of BDD

i. Facilitates strong collaboration:

BDD facilitates all the involved teams to have a thorough understanding of the project. They can easily carry out profitable discussions with flawless communication. BDD allows all the involved teams to connect with the product development cycle. Since it uses easily understandable language, all the teams can effectively write behavior scenarios.

ii. Provides high visibility:

The used language is understood by all, so everybody obtains proper visibility into the project’s development. The ubiquitous language is easily understood by both technical and non-technical parties. It eliminates errors and misunderstandings within teams. Consequently, it contributes to enhanced team productivity.

iii. Fulfills the user’s needs:

BDD helps the developers to fulfill the business needs which leads to satisfied users and a reliable business. As implied from the name itself, BDD focuses on the system’s behavior which lays a stronger influence than the implementation. The recurrent incidences of fulfilling the user’s need boost the confidence of the developers. When it comes to TDD vs BDD, teams using BDD are more confident than those using TDD.

iv. Comprehensive documentation:

In the BDD implementation, all those examples that stakeholders have come across in the discussions are documented. Hence, all the involved teams know the project’s progress. If an individual joins a team, they can go through these comprehensive documents and begin working on their tasks.

v. Cost-effective:

BDD improves the code’s quality which leads to reduced expenses in correcting the code’s errors. Thus, it decreases the costs of maintenance and minimizes the project’s pitfalls.

How does BDD streamline SDLC?

SDLC (Software Development Life Cycle) is referred to as a specification or a framework for any software development which defines system behavior or requirements.  It involves several stages to ascertain that the outcome meets the requirements. SDLC can be easy to implement if the defined requirements are easily understandable. Specifically, the BDD approach uses simple English to make sure the defined requirements can be easily understood by all the involved team members. Moreover, it offers multiple ways to depict real-world use cases for comprehending the requirements.

Another way in which BDD streamlines SDLC is by facilitating collaboration between developers, testers, and customers. It provides a platform enabling both technical and non-technical teams to seamlessly collaborate and interpret the requirements. Once the requirements are clear, it becomes straightforward to accomplish all the SDLC-related tasks.

Process of BDD

BDD guarantees that all development projects focus on fulfilling the business needs and also fulfil the user’s requirements. The process of BDD involves the following stages:

  • Describe the behavior: The team discusses the user story based on the requirements and examples.
  • Write test definition: The team writes test definitions based on the requirements and expected system behavior.
  • Run and fail: This stage involves running the test and determining whether it passes or fails.
  • Write code to make the test pass: This stage involves writing the code that can pass the test.
  • Run and pass: It involves running the test and acquiring the outcome.

You can understand the overall process of BDD with the following format of the acceptance test:

  • Given: This stage accepts the input from the user: a certain scenario
  • When: It denotes an action performed by the user
  • Then: It denotes the estimated system outcome

Here’s a practical example of the BDD process:

Given the user has entered a date in an invalid format on the form

When they click on the “submit” button

Then the form shows proper validation messages

Pros and Cons of Behavioral Driven Development (BDD)

Pros of Behavioral Driven DevelopmentCons of Behavioral Driven Development
1. Short learning curve
2. Reaches a broad audience
3. Improved communication between product owners, testers, and developers
4. No need to solve post-modification and post-deployment flaws
Improved quality code leads to reduced costs of maintenance and minimizes project risk
5. The use of ubiquitous language makes sure all teams have full visibility into the project’s advancement
6. Uses the low jargon and easily understandable approach
1. Doesn’t support the waterfall approach
2. Needs working experience in TDD
3. Less efficient for small development teams
4. Must be implemented at the project’s initial phase

What is Acceptance Test Driven Development (ATDD)?

Acceptance Test Driven Development (ATDD) is a software development practice focused on test automation. It is extended on the TDD approach to facilitate improved collaboration between testers, developers, and business participants. This test-first approach is frequently related to agile methodologies.

It makes the acceptance test cases the development’s foundation to focus on the end users’ requirements. Specifically, it aims to provide the agreed-on behavior/functionality of the system. In its implementation, the test is written from the user’s viewpoint and test cases are developed before the coding process begins.

There is no denying that there exist several similarities between ATDD and BDD approaches. However, BDD primarily focuses on the system’s behavior whereas ATTD focuses on the user’s requirements.

Benefits of ATDD

i. Prioritizes customer needs:

ATDD considers the user acceptance test criteria as the foundation for development. Therefore, customer needs are the central focus of the entire development process of ATDD. It helps developers exhaustively envisage the result. This leads to better coding and improved unit testing. It focuses on the end user’s need at each stage of development because it impels the developer to contemplate from a customer’s perception.

ii. Easy to manage:

The size of the team required for managing the ATDD development is small. The reason is this development takes place in multiple small iterations. Evidently, smaller teams are experienced and easy to build. They own the skills specific to the ATDD development process. With the ATDD approach, it becomes easy to manage infrastructure and resources, unlike the large development teams.

iii. Quick identification and resolution of issues:  

Testing is a crucial component of the software development process. It is vital to perform testing several times to check whether the created code meets the defined expectations or not. Therefore, it helps the developers to identify and resolve the issues at the earliest.

iv. Facilitates improved collaboration:

Collaboration begins as soon as the user story is written. It extends till the designed code fulfills the acceptance criteria. ATDD enables seamless collaboration between product owners, developers, testers, business analysts, cross-team members, and other business participants. With the help of the defined acceptance criteria and collaboration, all team members understand what must be achieved. So, they can ensure better fulfillment of the requirements.

Process of ATDD

Essentially, there is no definite approach to the implementation of the ATDD cycle. However, it usually involves four stages commonly found in all ATDD approaches. These stages are discussed below:

Stage 1: Discuss:

This stage of ATDD practice discusses the customer’s requirements. Simply put, it analyzes the end product which the customer expects from the development. To understand their expectations, testers and developers conduct a meeting with the clients/owners/business stakeholders of the product. They comprehensively discuss all the specifications and needs of the proposed feature.

Stage 2: Distill:

In this stage, tests are placed in a format that the testing tool can easily understand. It distills the simple English tests in a format that the system understands. Consequently, it becomes easy to implement tests within the development source codes.

Stage 3: Develop:

This stage implements the required features. ATDD uses a test-first development approach in this stage. Once the test code is written and validated, the developer executes the required features. Note that the developers would only implement the features after carrying out discussion and distilling (the previous two stages) and running the tests. The process iterates until pass/success is achieved.

Stage-4: Demo:

After implementing all the required features, the developers present a demo of the same to the business stakeholders.

Pros and Cons of Acceptance Test Driven Development (ATDD)

Pros of Acceptance Test Driven DevelopmentCons of Acceptance Test Driven Development
1. Improved collaboration between team members and cross-team members provides a thorough understanding of the system’s requirements
2. Assists in the documentation of software engineer’s code expectations into an executable format
3. Analyzes and discusses the real-world scenarios
4. Determines the acceptance criteria for the test scenarios
5. The acceptance test guides the entire software development process
6. All requirements are accurately analyzed leaving no chance of ambiguity
1. Needs exceptional expertise in bringing all team members on the board and convincing them to implement the approach
2. Complex learning curve

What’s BDD and How Does It Relate to TDD?

Behavior-Driven Development (BDD) is an Agile software development methodology that emphasizes collaboration between developers, QA professionals, and business stakeholders to ensure the software is developed with a focus on business value and customer needs. BDD expands on Test Driven Development (TDD) by incorporating a higher level of abstraction and using a natural language syntax that enables stakeholders to understand and contribute to the development process. BDD tests are written in a more readable, business-oriented language like Given-When-Then to ensure that tests are aligned with business requirements and that the development team is building the right software.

TDD vs BDD:

Both TDD and BDD are quite advantageous to streamline the software development process. Therefore, it is imperative to have a clear perspective on TDD vs BDD. Making a selection among the TDD vs BDD approach based on your project’s requirements can save you time and effort.

When discussing TDD vs BDD, we must first understand their similarities. Both of them intend to guide your software development process to improve usability and maintain product quality. Specifically, BDD aims to improve the collaboration between the development team and the business. On the other hand, TDD employs a continuous cycle of coding and testing to list specifications for particular software. This is a significant TDD vs BDD difference that clarifies the intentions of each of these approaches.

The following points comprehensively discuss the differences between TDD vs BDD framework:

  • Scope:

When it comes to determining the number of test cases, you can consider this point of difference between the TDD vs BDD framework. Usually, TDD spans a minor feature having a single unit test. Conversely, BDD spans a single behavior with a single test. A single behavior in the BDD approach may incorporate several components working collectively.

  • Documentation:

This TDD vs BDD difference is based on how easy it is to understand the tests. In TDD, unit tests function as technical documentation. It allows only developers to read and understand the tests. On the other hand, the BDD approach involves writing tests in non-technical language. Since the anticipated behavior of the application is explained in simple English, anyone can understand them. You can go through the real-world TDD vs BDD example to better understand how the two differ in terms of documentation.

  • The purpose behind testing

The comparison between TDD vs BDD approach is incomplete without knowing the testing purpose of each. TDD approach tests for functionality whereas the BDD approach tests for domain or design logic. To understand the purpose behind any testing, you can also go through any TDD vs BDD example.

Key Differences: TDD vs BDD vs ATDD

The following TDD vs BDD vs ATDD comparison table lets you narrow down your choice on the most pertinent development technique:

Parameters for comparison BDDTDDATDD
DefinitionBDD provides full test coverage based on the expected system behavior.TDD streamlines the software delivery process by developing the test case before the developers begin writing the codeATDD uses acceptance test cases to provide predetermined functionality of the system and fulfill end users’ requirements.
Key FocusSystem behavior, understanding of requirementsFeature implementation; unit testsDefining precise requirements, writing Acceptance Tests
Parties involvedCustomers, Developers, QAsDevelopersCustomers, Developers, QAs
Ease of understandingEasy for a non-technical person to understand itSince tests are technical, it is difficult for a non-technical person to understand itEasy for a non-technical person to understand it
Languages usedSimple plain English, GherkinProgramming languages like Python, Java, etc.,Simple plain English, Gherkin
Tools usedGherkin, Dave, RSpec, Behat, Lettuce, Specflow, BeanSpec, MSpec,  JBehave, Concordian, Cucumber with Serenity / Selenium  Cucumber, JDave, JBehave, BeanSpec, Gherkin Concordian, Spec Flow, Junit, TestNG, FitNesse, NUnit frameworks, Selenium tool (any open source tools)FitNesse, TestNG, Spectacular, Concordian, EasyB, Robot Framework, Thucydides, FIT
Project compatibilityProjects in which the user is handling e-commerce websites or different types of apps.Projects that don’t need the involvement of end users like API, server, etc.Projects targeted at customer experience; Projects with high competition like apps and e-commerce websites
BugsMore difficult to track down compared to TDDCan be easily tracked down and reduced the occurrenceDifficult for developers to track them down

It’s Not About TDD vs BDD vs ATDD – How Do They Work Together?

It is not mandatory to use only one specific development technique. Based on your project’s requirements, you can combine any two of these three techniques. So, it’s not always about comparing TDD vs BDD vs ATDD, but you can use them in different combinations to gain the maximum advantage.

When you combine these three development techniques, you don’t merely write tests from the developer’s code-centric perspective. Essentially, the combination of these three techniques helps you to:

  • Bring parties on board
  • Establish conversations
  • Ascertain that everybody can help improve the app’s/software’s quality by discussing their perceptions

Hence, the combination makes sure your developed application/software can effectively fulfill its requirements and you can increase your product development cycle’s efficiency. Furthermore, this combination facilitates the QA team to emphasize more challenging test cases. Overall, this combination helps all the team members to work more efficiently and gain all the benefits of each technique rather than simply comparing the TDD vs BDD vs ATDD.

Which One to Choose Between TDD, BDD, and ATDD?

The following points provide you with a broad perspective on which one to choose from TDD vs BDD vs ATDD.

  • The BDD testing method is more suitable for e-commerce projects.
  • TDD testing method is more suitable for projects that don’t involve end users like APIs or servers.
  • ATDD testing method is more suitable for working on developing app projects.

Initially, it may seem complex to implement any specific development technique. But meticulously selecting the right technique based on your project’s requirements and anticipated outcomes will save time on the overall development process. Moreover, careful selection enhances the quality of the end product.

A combination of all three or two of them provides outstanding opportunities for conversations, collaboration, and enough insights into the end product’s specifications.

Summary

The present blog post discussed the three testing practices –TDD, BDD, and ATDD that streamline the software development process.  They predict the user’s requirements, determine the code to write, and use different test cases. Consequently, they make sure software development advances on the correct path and ultimately boosts the overall productivity of the software development team. You can choose any of these test practices after taking into account the requirements of business and end users, and the anticipated outcomes.

Frequently Asked Questions

Is Selenium BDD or TDD?

Knowing whether Selenium is BDD or TDD helps you to better compare TDD vs BDD. Selenium helps to automate UI test cases. When you use it for test automation, it applies software development processes that enhance test-driven development and allow object-oriented, domain-driven analysis.  In the TDD’s formulation phase, models are documented so that they can easily automate testing and development.

What is the example of TDD and BDD?

You can go through the TDD vs BDD example to simplify the choice between these two development techniques.

Here’s an example of BDD:

Given: User navigates to Google homepage

When: User entered “Programming” in the search engine

Then: Click on the search button

Outcome: The search results for Programming are displayed in the web browser

Here’s an example of TDD:

Suppose you want to buy a car. You will follow the below steps that imitate the TDD approach.

  1. Firstly, you check the prices of different cars online but realize that you don’t have sufficient money to buy the desired car (resembles a “Fail” state).
  2. You work hard to gather the required money, then you visit the car shop and buy your desired car (resembles a “pass” state).
  3. After a few months or years, you wish to buy another car and so, you try finding a more efficient way to earn the required money (resembles “refactor” state).

Is BDD the same as Agile?

BDD is not the same as Agile but it supports the agile methodology by delivering constant input from the end user’s perception. On the other hand, Agile methodology is coined to abridge the software development cycle. It makes it easier for organizations to deliver faster releases. Unlike BDD which doesn’t support constant feedback, Agile methodology incorporates a cycle of constant feedback when a product is under development.

Is TDD an SDLC?

Software Development Life Cycle (SDLC) is a process that designs, develops, and tests high-quality software. It aims to produce high-quality software that fulfils or surpasses customer expectations.  Cost-effectiveness and speed are the two key aspects that SDLC focuses on.

You can consider TDD an SDLC since TDD develops the test cases to streamline the software delivery process.

What are the types of TDD?   

Two types of TDD are discussed below:

i. Acceptance TDD (ATDD): ATDD helps you to write a behavioral specification or a single acceptance test based on your chosen terminology. Subsequently, you only need the required product functionality to accomplish that test.

ii. Developer TDD: Developer TDD helps you to write a single developer test. You only need the necessary product functionality to perform the test. TDD aims to state a comprehensive, executable design for your product on a JIT basis.

Suggested Readings

Test Driven Development

BDD with Gherkin

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