TDD (Test Driven Development) and BDD (Behavior Driven Development) are both modern ways of testing software. These methodologies are widely employed by developing agencies that work on Agile principles. Both TDD and BDD have their advantages, and hence are chosen for different reasons. Programmers who adopt traditional development methods, always leave testing for the last. Testing is usually seen as an ‘extra’ activity and even considered wasteful of a company’s resources. TDD and BDD models have been designed to oppose this backwardness and assert the true purpose.

Test Driven Development

TDD is a software development approach that involves writing of automated test cases  before writing the functional code. Using TDD for creating software applications is a great way to guarantee elimination of bugs and errors from the beginning. As most of the code is tested automatically, it is cleaner and results in a high quality end product. Developers use an inside-out perspective and focus on unit tests to check if their code is correct.

The requirements of the project in question are set out. Each requirement is taken and converted into a particular test case. This practice allows developers to concentrate on required features before initiating the coding process. It helps eradicate the need for updates and alterations at later stages of development. The concept of TDD can be outlined in six simple steps:

  1. Write a test or Add a test
  2. Run the test and see it fail
  3. Write code to pass the test
  4. Run the new/amended tests
  5. Refactor your code (optional)
  6. Repeat from step #1

Starting with TDD feels like putting in a lot of extra time, effort, and resources, but the way it pays off later compensates for everything. With more than 90% test coverage, the code becomes maintainable and making changes causes zero issues. This is because a substantial set of test confirms that your code is stable and will not break due to minor alteration. Developers have a hard time adhering to TDD as it is completely opposite to traditional activity; writing tests before writing the actual code may strike as preposterous.

So once a requirement is converted into a well described test, the developer can grasp the essence of what’s requisite. In the next step the tests are supposed to fail because none of the features are actually implemented. If your test passes, it probably means you have made an error. Another possibility is that the test’s required behavior already exists, so you don’t have to write that code.

Finally the moment arrives when the developer has to write the actual functional code. The code does not need to be of very high quality, but good enough to be compatible with tests written. Then the tests are run again, and if they all pass it means that your code meets the requirements, causing no collateral damage. If all the tests do not pass, you need to fix or adjust your code accordingly.

Once all the tests are cleared, the code needs to be refined or tidied up a bit before deployment. Generating high-quality code and meeting market standards is the objective of testing after all. The steps are repeated for every other requirement or even for the same one if you feel that it could use improvement. TDD is expensive when done correctly, but it saves us from bigger costs that are exposed later, as a consequence defective code.

Behavior Driven Development

Unlike TDD, BDD is all about an outside-in perspective, which makes it rather confusing. It focuses on business or user behavior that your code is implementing, i.e the ‘why’ behind your code. This methodology works well in an Agile environment and should be used in combination with TDD and Unit testing. Although the preceding steps of BDD are different from TDD, the postliminary stages are practically the same.

The main contradiction lies in the demand of a business analyst. The process usually involves collaboration between the Agile product owner and the business analyst. These two have to sit together, have discussions and generate a list of specifications. They evaluate how new features may break, transform or improve the current workflow of a system.The developing team takes note and adds other technical requirements through their own understanding; the rest is pretty much the same as in TDD.


While TDD relies on user stories that define what has to be tested, BDD further elaborates these stories by telling why and how these things need to be tested. Therefore BDD gives developers a better idea and a bigger picture of what the client desires. TDD almost entirely relies on the input of a developing team, whereas BDD provides a more collaborative approach by including testers and business stakeholders. Also, BDD applies simpler language so everyone involved is on the same page. The outcome is not assessed on mere functionality, but upon how it would influence the business. Concluding that BDD is kind of an extension of TDD, it is a bit more complex and difficult to execute.

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