What is the difference between TDD vs BDD?

tdd vs bdd - difference

18 March 2021 Stephan Petzl Leave a comment Development

TDD and BDD are two types of software development practices. TDD stands for test-driven development, while BDD is a short form of behavioral-driven development. The names of both sound similar, but of course, they are not! Please do not get them confused.

A brief explanation of TDD: we specify what a program should do by writing code that can directly be executed; On the other hand, in BDD, we define the behavior for a program with natural language. These behaviors can not be directly be executed.

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

What is TDD?

TDD means test-driven development. In this software development technique, you 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 used in combination with test automation.

The team that implements TDD requires more time to develop the software, but it can improve the software quality significantly.

Also, the code is more flexible and can be more easily reused. Besides that, TDD supports achieving high coverage of tests, about 90 to 100 percent.

Developers who follow TDD often claim that the most challenging task is to write their test cases before writing the code.

what is tdd
Example of a login test routine that is written before the implementation of the code. The language for this test is Kotlin.

Step-by-step TDD Process

  • Write the test cases – First of all, you need to write an automated test case depending on the requirements.
  • Run the test cases – Now you need to run all these test cases on the code you’ve developed recently.
  • Correct test cases – If the test case doesn’t work, then you need to edit the test code to allow that test case to work as expected.
  • Rerun test cases – Rerun all of the test cases and notice that all the developed test cases are working or not.
  • Refactor your code again – This one is optional and can be skipped if you want. However, readability and reusability can be improved by refactoring.
  • Repeat all of the above steps for new test cases – Repeat all of the steps mentioned above for other test cases until you see that all the test cases have been implemented.

Example of TDD implementation

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

  1. Write your first test. Name it “shouldLoginUser”
  2. Run the test, and an error will show up, indicating that functionality has not yet been implemented
  3. Develop the application code to get your test working: Some routine which will read the username, password check them, and return a “valid” or “invalid” depending on the input.
  4. Rerun the test case, and if you implemented everything correctly, your test will pass.
  5. Check if you can improve your code.
  6. 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.

Have a look at TDD framework representation.

Example of TDD Implementation

Benefits of TDD

Here we have listed the benefits of Test-Driven Development for your better understanding.

Criteria of acceptance

When you write a new code, you usually have a list of required features and acceptance criteria needed to be met. Any of these can be used for what you are required to test, and then when you’ve got that list, you can be relaxed if it confirms that you haven’t missed anything.

Better focus

Developers are more productive while coding; TDD supports keeping productivity high by facilitating your focus.

If you write a failing test, then you’ll focus only on that to clear that test. It enhances you to consider smaller stuff related to functionality for the time being. Instead of handling the bigger picture, it may result in more errors and a long time for development.


Just because you are writing a test for single functionality, writing a test means that you need to pay attention to the public interface that another code in the application requires to integrate. You do not consider the private methods or internals that you are about to start working on.

From the test perspective, you’re writing methods to test the public ways. It means that the code will make more sense.

Clean code

Your test can only interface with the public methods of your codebase, which means that you have a better idea of what can be made private. It means you do not expose the methods accidentally, which are not required to be public. If you accidentally made parts of your APIpublic, you may probably have to support that in the future.

Safer reorganizing

Once you have passed a test, it’s now safe to reorganize your codebase. Keep in mind that the test cases have your back. If you are required to work with legacy code or the code that somebody else has written, with no tests been written, TDD can still be practiced.

Fewer 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.

Not to mention that you may be able to think of every test case, but if a bug shows up, you can continue with the test before you attempt to rectify the error.

Also Read: Repeato’s mission: Why I Chose to Write my Own UI testing tool

What is BDD?

BDD means behavioral-driven development. It is an extension to TDD, where you start by describing behavior instead of writing test cases. We develop the codebase afterward, which allows our application to perform the expected and described behavior.

The scenario explained in the BDD approach makes it convenient for the testers, developers, and business users to collaborate. BDD is considered a great practice when we talk about automated testing. It mainly focuses on the application’s behavior and abstracts from code implementation.

The application’s behavior is the center of focus in BDD. It forces the testers and developers to put themselves into the shoes of the user.

What is BDD - behavioral-driven development


Step-by-step BDD process

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

  • Write the application’s behavior – An application’s behavior must be written in simple English, like instructions written by a product or business analyst’s owner.
  • Write automated scripts – This simple easy to understand language then gets converted into programming tests. This can be accomplished either manually or by automatically generating a test script based on the original behavior description.
  • Code implementation – Now the functional code which enables the software behavior gets implemented.
  • Check if the behavior succeeds – Now you need to run the behavior and check if it is working. If working, move towards the next behavior. If not doing so, rectify the errors in the functional code for achieving the application behavior.
  • Organize the code – Organize or refactor your codebase to make it readable and to be reused.
  • Repeat all of above steps for new behavior – Repeat all the steps mentioned above for implementing more behaviors 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 a submit button.

  1. Write the behavior of the application: What should happen if a correct Username and Password are entered into the form?. Example: “When a user goes to the login form and puts in a correct username and a correct password and then clicks login, they should be redirected to the home screen”
  2. Now write an automated test script for that behavior
  3. Implement the code.
  4. Run this behavior 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 behavior and follow all of the above steps for this new behavior.

Benefits of BDD

Here we have listed a detailed list of benefits of Behavioral Driven Development for your better understanding

Strong collaboration

In BDD, all of the people involved have a better understanding of the project. All of them can communicate and have constructive discussions without any obstacles. BDD improves and increases collaboration. It allows the people involved in the project to engage with the product details.

Great visibility 

Suppose the language of communication is easy to understand for everyone participating. In that case, people experience strong visibility into the progress of the project.

Software design follows the business value

BDD puts a great value on the business needs and requirements. When setting priorities with your client, depending on the values they provide, developers can deliver a better result when they have a better understanding of how a client thinks.

Ubiquitous language

Ubiquitous language is that language that every member can understand easily. It reduces the possibility of misunderstandings and misconceptions and makes it convenient for those who join the group later.

Software meets user needs

When you focus on business needs, you will have satisfied users, which implies a flourishing business. With BDD, you tend to focus on the behavior better, which leaves a strong effect than implementation itself.

Better confidence

People who use BDD are generally more confident as there is no chance to break the code. When it comes to their work, they have better predictability.

Lower cost

When you improve the code’s quality, you reduce the maintenance cost and minimize the project’s risk factor.

Most people get confused for not having a better idea about the difference between TDD and BDD. TDD requires you to use code as a language to describe your test cases. In comparison to that, BDD is a language that allows users to understand and use it easily as it is like general language.

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

What is better: TDD or BDD? 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 expected.
  2. In TDD, developers use programming language, and in BDD, readable scenarios are written in simple words.
  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; however, scenarios do not get affected by functionality changes.
  5. TDD may be the better approach for projects which involve third-party tools. But BDD is the better approach for projects which involve more stakeholders, like UX designers, project managers, and so on
  6. Tools that support TDD are TestNG, NUnit, JUnit, etc., and Tools that support BDD are MSpec, Cucumber, Specflow, etc.
  7. Only developers can understand TDD tests. In contrast, BDD tests are easy to understand for ordinary people who don’t have a coding background.
  8. TDD reduces the risk of errors in your tests, while in BDD, errors are difficult to track when comparing that with TDD.

In a nutshell

Selecting between TDD and BDD seems to be tricky. Some may believe that TDD is better as it supports efficient test creation for developers without going through the hassle to implement another level of abstraction BDD. On the other hand, some say that BDD is the right choice of strategy, cause it brings all the stakeholders on the same page.

No approach is better than the other; it depends on the developer which methodology is convenient for him personally, like the TDD method or the BDD method.

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