BDD is designed to test an application’s behavior from the end user’s standpoint, whereas TDD is focused on testing smaller pieces of functionality in isolation.

TDD stands for Test Driven Development. In TDD, the test cases are created first and then the code underlying those test cases are written. Although TDD is a development technique, it can also be used for automation testing development.

The teams that implement TDD, take more time for development however, they tend to find very few defects. TDD results in improved quality of code that is more reusable and flexible.

TDD also helps in achieving high test coverage of about 90-100%. The most challenging thing for developers following TDD is to write their test cases before writing the code.

TDD is a development practice while BDD is a team methodology.

Process Of TDD

TDD methodology follows a very simple 6 step process:

1) Write a test case: Based on the requirements, write an automated test case.

2) Run all the test cases: Run these automated test cases on the currently developed code.

3) Develop the code for that test cases: If the test case fails, then, write the code to make that test-case work as expected.

4) Run test cases again: Run the test cases again and check if all the test cases developed so far are implemented.

5) Refactor your code: This is an optional step. However, it’s important to refactor the code to make it more readable and reusable.

6) Repeat the steps 1- 5 for new test cases: Repeat the cycle for the other test cases until all the test cases are implemented.

Benefits of Test-Driven Development

• Helps reduce the amount of time required for rework.
• Helps explore bugs or errors very quickly
• Helps in getting 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

What Is BDD?

BDD stands for Behavior Driven Development. BDD is an extension to TDD where instead of writing the test cases, we start by writing a behavior. Later, we develop the code which is required for our application to perform the behavior.

The scenario defined in the BDD approach makes it easy for the developers, testers and business users to collaborate.

BDD is considered as the best practice when it comes to automated testing as it focuses on the behavior of the application and not on thinking about the implementation of the code. The behavior of the application is the center of focus in BDD and it forces the developers and testers to walk-in the customer’s shoes.

Process Of BDD

The process involved in BDD methodology also consists of 6 steps and is very similar to that of TDD.

1) Write the behavior of the application: The behavior of an application is written in simple English like language by the product owner or the business analysts or QAs.

2) Write the automated scripts: This simple English like language is then converted into programming tests.

3) Implement the functional code: The functional code underlying the behavior is then implemented.

4) Check if the behavior is successful: Run the behavior and see if it is successful. If successful, move to the next behavior otherwise fix the errors in the functional code to achieve the application behavior.

5) Refactor or organize code: Refactor or organize your code to make it more readable and re-usable.

6) Repeat the steps 1-5 for new behavior: Repeat the steps to implement more behaviors in your application.

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:

TDD Vs BDD – Key Differences

TDD	BDD
Stands for Test Driven Development.	Stands for Behavior Driven Development.
The process starts by writing a test case.	The process starts by writing a scenario as per the expected behavior.
TDD focuses on how the functionality is implemented.	BDD focuses on the behavior of an application for the end user.
Test cases are written in a programming language.	Scenarios are more readable when compared to TDD as they are written in simple English format.
Changes in how the application functions impact a lot on the test cases in TDD.	BDD scenarios are not much impacted by the functionality changes.
Collaboration is required only between the developers.	Collaboration is required between all the stakeholders.
Might be a better approach for projects which involve API and third-party tools.	Might be a better approach for projects which are driven by user actions. For eg: e-commerce website, application system, etc.
Some of the tools which support TDD are: JUnit, TestNG, NUnit, etc.	Some of the tools which support BDD are SpecFlow, Cucumber, MSpec, etc.
Tests in TDD can only be understood by people with programming knowledge.	Tests in BDD can be understood by any person including the ones without any programming knowledge.
TDD reduces the likelihood of having bugs in your tests.	Bugs in tests are difficult to track when compared to TDD.

Conclusion

Choosing between TDD Vs BDD can be very tricky. Some might argue that BDD is better for finding bugs whereas the others might just say that TDD gives higher code coverage.

Neither methodology is better than the other. It depends on the person and the project team to decide on which methodology to use.

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

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.

Differences: TDD vs BDD vs ATDD

Tools used

JDave, Cucumber, JBehave, Spec Flow, BeanSpec, Gherkin Concordian, FitNesse

Gherkin, Dave, Cucumber, JBehave, Spec Flow, BeanSpec, Concordian

TestNG, 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.