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What are the differences between TDD & BDD.

Lets see some of the Differences between TDD and BDD approach.

TDD and BDD are two types of software development techniques. TDD stands for Test-Driven Development and BDD stands for Behavioral-Driven Development. The names of them both sound similar but they are not similar.

What TDD and BDD?

We show what a program should do by writing code that can be executed directly. On the other hand BDD, we define behavior of a program in human friendly language. This program cannot be executed directly.

Before discussing the differences between these two in detail, let’s first explore what TDD and BDD ?

What is TDD?

TDD means test driven development, in this software development technique. In This we initially create the test cases and then write the code to fulfill those test cases. TDD is a software development technique. It can also be in Combination of test automation.

It requires more time to actually develop the software by the team and it can also improve the quality of the software more significantly.

The code can be easily reused and is more flexible and it supports high coverage of testing about 90-100 percent easily.

What is so challenging about the TDD approach?

It is actually challenging for the team to write test cases before writing the code in TDD approach.


End to End process of TDD approach

  • Writing the test cases: Firstly, you have to write the automated test cases before writing the code depending on the requirements given.

  • Run the test cases: Now, you need to run the test cases on the code you have recently developed.

  • Correcting the test cases: You will be correcting the test cases by editing the code if it doesn’t work as per requirements. After editing you check if it's working as expected.

  • Rerun all the test cases: You will rerun and check if all the developed test cases are working properly or not.

  • Refactor your code again:This step is optional and can be skipped if you want. But, readability and reusability can be improved by using this step called refactoring.

  • Repeat all the above test cases for new Test cases : Repeat the steps above for other test cases until you see all the test cases have been implemented.

Example of TDD Implementation:

Suppose you have to develop a login functionality for some application using username,password option and submit button

  • Write your test as “Signin”

  • Run the test, and an error will show up, indicating that functionality has not yet been implemented.

  • To get your test working, develop the test case implementation. It will read the username, password check them, and return a “valid” or “invalid” depending on the input.

  • Rerun the test case, and if we have implemented everything correctly, your test case will pass.

  • Check if you can improve your code.

  • Now write a new test case using an empty username and Password.

If this method to run the test case is applied, it will fail. Repeat all the initial five steps for this test case and then add the functionality for handling empty Username and Password.

Representation of TDD framework:

Benefits of TDD:

Here, are some of the benefits of TDD (Test-Driven Development) approach as mentioned below:

  • Acceptance : When you write a new code, you usually have a list of requirement features and acceptance criteria needed to be met.

  • Focus :TDD supports by keeping the productivity high and by having better focus.

  • Interfaces : For single functionality it's important to focus on the public interface that another code in the application requires to integrate.

  • Clean code :Only public methods are used in the code in interface, which means that you will have a better idea of what can be made private or public.

  • Safe reorganizing :Once you have passed a test, it’s now safe to reorganize your code. If you are required to work with code that somebody else has written, with no tests being written, TDD can still be practiced.

  • Better design: It enables programmers to take their time to consider the design or the primary specifications for the finished product before creating the main code.

  • Very less bugs :TDD often results in more tests, which may result in longer times for test runs. On the other hand, you can save a lot of time with better code coverage: Errors are found and fixed a lot quicker this way.

What is BDD?

BDD means behavior Driven Development. It is an extension to TDD where you start by describing behavior instead of writing test cases. We develop code afterwards which allows our application to perform the expected and described behavior.

BDD approach makes it convenient for the testers, developers and business users to collaborate. BDD approach is a great practice when we talk about automated testing. It is mainly dependent on application behavior and abstracts from code implementation.

In BDD the focus is on Application’s behavior it forces the developers and testers to clearly understand the behavior of the application.


Feature File in Gherkins language

The above required glue code or step definition is the executable test code of the feature file.

End to End BDD process

The process followed for BDD methodology is also a six-step procedure similar to the TDD cycle.

  • Write Application’s behavior – The behavior or feature file of the application must be written in simple natural English language.

  • Write automated scripts – This simple easy to understand language called Gherkins then gets converted into programming tests. This can be accomplished either manually or by automatically generating a test script based on the original feature file or behavior description.

  • Code implementation – Now the functional code which enables the software behavior or feature files gets implemented.

  • Check if the behavior succeeds – Now you need to run the feature file and check if it is working. If working, move towards the next feature file. If not working , rectify the errors in the functional code for achieving the application behavior.

  • Organize the code – Organize or refactor your code to make it readable and to be reused.

  • Repeat all of the above steps for new behavior – Repeat the steps mentioned above for implementing more behaviors or feature files in the application.

Example of BDD implementation

Suppose that, for an application, you are required to develop a software functionality that has fields to fill in the Username, Password, and confirm password and a submit button.

  1. Write the behavior of the application: What should happen if a correct Username, Password and confirm password are entered into the form Example: “When a user goes to the Register form and puts in a correct username, correct password and correct confirm password then clicks login, they should be redirected to the home screen”

  2. Now write an automated test script for the same feature file.

  3. Implement the code.

  4. Run the same feature file and check if it works. If it does, then move to step five and otherwise rectify the implementation and then rerun it all over.

  5. Refactoring the implementation is optional, and you can skip this step if you want. In this case, you can reorganize the code in the submit method for printing the error messages.

  6. Now write a different feature file and follow all of the above steps for this new feature file.

Benefits of BDD

Here are the list of benefits of Behavioral Driven Development

  • Strong collaboration: BDD improves and increases collaboration. It allows the people involved in the project to engage with the product details. The whole team will have a better understanding of the project.

  • Better visibility :Language is the key. The Language to communicate is easy to understand for everyone participating in the team. In that case, there will be strong visibility into the progress of the project with the team.

  • Software design follows the business value: When setting priorities with your client, depending on the values they provide, developers can deliver a better output .BDD puts a great value on the business needs and requirements.

  • Easy language: BDD approach uses easy Gherkins language. It reduces the possibility of misunderstandings and misconceptions and makes it convenient for those who join the team in later stages also.

  • Software meets user needs: With BDD, you can focus on the behavior better, which leaves a strong effect than implementation itself. When you focus on business needs, you will have satisfied users, which helps business to grow.

  • Better confidence: The team which uses BDD approaches are generally more confident as there is no chance to break the code. They have better predictability and better understanding of the code.

  • Lower costs: With great code’s quality, you reduce the maintenance cost and minimize the project’s risk factor.

TDD and BDD have little similarities with so many differences. Let’s explore the details about both the approaches TDD vs. BDD below.

Test-Driven development vs Behavior-driven development

  1. The TDD test begins by writing a test case, while the BDD test begins by explaining a scenario as required.

  2. In TDD, developers use programming language, and in BDD, readable scenarios are written in simple Gherkins language with easy keywords like Given, When, Then, And

  3. TDD focuses on implementing the functionality, while BDD uses the application behavior for the last user.

  4. Variations in the application functions impact the test cases in TDD; but in BDD scenarios do not get affected by functionality changes.

  5. For projects which involve third-party tools TDD may be a better approach. But BDD is the better approach for projects which involve more stakeholders, like designers, project managers, etc.,

  6. Only developers can understand TDD tests. BDD tests are easy to understand even by an ordinary person who doesn't have a coding background or knowledge.

  7. TDD reduces the risk of errors in your tests, while in BDD, errors are difficult to track.

  8. Tools that support TDD are TestNG, NUnit, JUnit, etc., and Tools that support BDD are MSpec, Cucumber, Specflow, etc.


Selecting TDD or BDD approaches seems to be tricky. Some may believe that TDD is better as it supports efficient test creation for developers without going through the tough job of implementing another level of abstraction like in BDD. BDD is the right choice of strategy, because it brings all the team members on the same page. No approach is better than each other. It depends on the developers, stakeholders, testers and entire team to select which approach is better for their project according to their requirements and time.

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