BDD vs TDD. Know the difference


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Over the past decade, software development processes have evolved a lot. From the waterfall model to agile to DevOps, the approach keeps on getting better and better. This change has also brought test-driven development approaches to get fewer bugs in the software/application/product getting developed. TDD and BDD are the two most popular test-driven development approaches.

In this blog, I will talk about these approaches briefly and explain the differences between BDD vs TDD. 

TDD stands for Test-Driven Development and BDD stands for Behavior Driven Development. They are the practice of building code tests for applications. More specifically, they are software development processes in which you create a test that sets an expectation before implementing any code.

What is Behavioral Driven Development (BDD)?

Behavioral Driven Development is a software development approach which is an extension to the test-driven approach where you write the tests focused on user and system behavior before developing the application. After the tests are ready, developers code for the application. It can be written in a shared language like English so that it is easy for a technical, non-technical or a stakeholder to understand. 

In BDD, you start off with writing about behaviors. Imagine when your product owner or CEO of your company asks you about a test which you have written for a particular feature, you cannot show him the Junit or the integration test. They might not understand because you might be writing each feature in a different language.

The main idea about BDD that it says nothing about implementation. It is purely focused on the customer’s experience when they use the software. You try to capture what the customer thinks they want in the form of user stories, which are lightweight descriptions of how the app is going to be used. Some people call these use cases. 

In BDD, you basically ask questions about the behavior of the app, which is what the customer sees before and during development. This is done to reduce the chance of misunderstanding with the customer about what is actually to be built. 

Pros of BDD

  • It increases and improves the collaboration between the stakeholders. The communication between product owners, developers, testers happens smoothly in BDD.
  • It provides better clarity of the scenarios required for the development. It is written in Gherkin language (simple text), which is easily understandable to a non-technical person also.
  • This approach is very user-focused and providing an amazing user experience is the priority. A happy user has a good impact on the business of the organization.
  • Writing the test cases in plain English language reduces the chances of misconception and misunderstanding of requirements.
  • It can be easily integrated with plugins like Cucumber for automation testing by creating automated test scenarios.

Cons of BDD

  • Since this approach is very much dependent on the client/user, their availability is a challenge. In case there is any ambiguity in any test scenario, the client/user must be available for a discussion to get more clarity on the requirement.
  • If there are many features involved in creating a big application, managing the test files on all the features can be a headache. A good naming convention is recommended in such cases.
  • If there is a lack of communication between the user story creator and developers, the organization can end us designing a product that would be very different than the requirement given by the client. Also, if the teams involved are working remotely, then there is a big risk.
  • All the requirements are not known at the beginning when you start working on the BDD tests and sometimes requirements get modified also. In that case, the tests have to be written again later in case of any requirement addition or change.

What is Test-Driven Development (TDD)?

Test-Driven Development is a software development approach which works on test-first development, where we write a test before we write code. TDD can be defined as a programming practice that instruct developers to write new codes only if an automated test has failed. This avoids duplications of code. 

The primary goal of TDD Is to make the code clearer, simple and bug-free. TDD relies on a very short development lifecycle. Once all the test pass, it signals the end of the iteration. If there are more features that need to be implemented in your product, the product will go through the same phase again, but this time with a new feature and it will have more tests.

Pros of TDD

  • It helps you become better at writing good code. When you write the unit test first and then you write the code to make those unit tests pass, you are basically starting out by defining the API which is really valuable for writing clear quality code that is easy to understand.
  • Since you write the test cases before coding for the application, refactoring the tests becomes faster and easier.
  • Because you create multiple small test cases before building a complete product. It teaches you to write modular codes depending on each test case, which is a good development principle.
  • It saves a lot of QA testers time because a lot of stupid mistakes are identified by the developers when they run the TDD test cases on the code they develop.
  • The unit test cases and its results act as documentation. The other developers can easily look at the tests and the code developed to understand the requirement.


Cons of TDD

  • Writing good test cases is an art and it may take some time to write good test cases. This can slow down development.
  • If you already have a big existing system with a huge legacy code, writing test cases would be very difficult.
  • Everyone on the team working on TDD and writing test cases must be equally well skilled in writing and maintaining the tests. If it is not the case, the test-driven development can quickly fall.
  • If the features are constantly changing, the test cases must be modified as well. This can be really time taking if the features are very dynamic in nature.


Key differences between BDD and TDD

Although both the software development approaches, TDD and BDD are similar and many ways, they are still different. Below is a list of key differences between TDD and BDD:


Stands for Test-Driven Development Stands for Behavior Driven Development
Focuses on writing tests for functionalities Focuses on writing tests for behaviors
This process involves collaboration between developers This process involves collaboration between product owners, developers, QA engineers, customers
Witten in a language similar to the language used for functionality development – java, python etc. Written in simple English language – gherkins
This process starts by writing the test cases This process starts by writing user stories for the behaviors required from the application
In TDD, the client has no update until some development happens Here the client knows what is getting developed because a lot of interactions happen to understand the user behavior in detail
Coding and refactoring are the major two stages involved Features discussion, creating user stories, testing, coding, refactoring are the stages involved
Better suited for projects involving lot of
API interactions
Better suited for applications with heavy user actions like ecommerce website, mobile apps etc.
Popular TDD tools are Junit, PHPUnit, TestNG, csUnit, PyUnit Popular BDD tools are Cucumber, JDave, Concordion, SpecFlow
Only technical folks like developers can understand TDD as it requires programming knowledge Both technical as well as non-technical person can understand and work on BDD
You can expect fewer bugs in your tests Chances of having bugs are more as compared to TDD


Final Thoughts

Both TDD and BDD are very important approaches to software development. I hope after going through this blog, now you would be having a better understanding of Test-driven development and Behavior-driven development than before. You also understand now the differences between the two. 

There is no clear-cut answer to tell you which one is better. BDD is treated as an extension of TDD, but that doesn’t mean BDD has to be a clear winner. TDD will focus on the technicalities of the requirement whereas BDD will focus more on collaboration go stakeholders and ultimately delivering the product with a good user experience. Both the software development approaches are used depending on the kind of project you are working on or the type of application your client wants you to build. So, depending on the task at hand, you should decide on choosing which approach will be better. 


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