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BDD vs TDD what's the debate all about?
Posted On: 22 November 2021

The software development world suffices a host of debates, and the BDD Vs. TDD is one of those that continues to rage on.

Consider this; the world’s first-ever software was written and executed in 1948. This amazing innovation correctly computed the value of 218 in “only” 52 minutes.

Since those early days, software development has come a long way and set a strong foundation for the modern digital economy. As such, it has transitioned from the traditional waterfall approach to an agile approach. Likewise, it has shifted from Test-driven Development (TDD) to Behavior-driven Development (BDD). Or has it?

Since 2018, the inclination towards BDD has increased by 60%. The use of BDD in scripting and test automation is growing rapidly.

So, the facts indeed suggest organizations parting ways with TDD; however, the scenario is much more intricate than it appears. To explore the same, we have to answer these questions.

TDD and BDD: The Similarities

Before exploring the TDD vs. BDD debate, it’s important first to unpack the meaning of TDD and BDD and understand their commonalities and differences.

Both TDD and BDD are testing methods to find bugs and correct issues in software applications. Also, in both forms, test writing happens before code writing.

These similarities notwithstanding, TDD BDD are different approaches to testing.

What is the Difference between BDD and TDD?

Test-driven Development

Test-driven development or TDD means that a developer writes a test for functionality and runs it to see it fail because the functionality doesn’t exist. Then they would write code to make the test pass. Finally, after refactoring code and repeating this “Red-Green-Refactor” loop multiple times, they would have code that creates a complete feature.

The TDD testing methodology is implemented from a developer’s perspective. They write automated test cases before functional pieces of code. The goal is to understand “is this code valid?” If it’s not, the test will fail. Only then will the developer refactor the code, i.e., change it without modifying its key behavior. They then run the test as many times as needed for it to pass successfully.

Behavior-driven Development

Behavior-driven development (BDD) is derived from TDD. Like TDD, BDD is also a “test-first approach.” However, unlike TDD, BDD involves multiple stakeholders, such as developers, test engineers and testers, Product managers, and users, who work together to ideate various acceptance criteria in a user’s story.

Also, BDD takes a different approach to software testing since it tests the system’s actual behavior from the end users’ perspective. Thus, in BDD, tests are written using a “Given-Then-When” behavioral approach:

Given a user does  X | When a user clicks on Y | Then display Z

These behavior examples are described in a simple “shared language” such as English or a domain-specific language for writing behavior scenarios, such as Gherkin. The examples are then converted into executable specifications by developers.

The TDD vs. BDD Debate

The TDD vs. BDD Debate

Essentially, the BDD vs. TDD debate boils down to “Which is better? – TDD or BDD, or vice versa?”

BDD and TDD are both testing strategies where the tests are used as part of an automated testing framework. However, they differ in scope. So, before adopting either approach, developers should ask, “What am I testing for?”

BDD and TDD are both testing strategies where the tests are used as part of an automated testing framework. However, they differ in scope. So, before adopting either approach, developers should ask, “What am I testing for?”

Answer 1: The software’s implementation.

Choice 1: TDD

Answer 2: The software’s behavior.

Choice 2: BDD

In TDD, the tests will fail when a functionality doesn’t exist. But as new code is written (refactored), the system will evolve until the complete feature is obtained, at which point the test will pass. In comparison, BDD testing looks at a system’s behavior to understand how it will behave when certain conditions are realized.

Since TDD is developer-focused, tests are written by the developers. That explains why it predominantly focuses on testing smaller pieces of functionality in isolation. Contrarily and as elucidated above, BDD tests an application’s behavior from the user’s perspective, which is why the automated specifications are created by users or testers, not by developers. Moreover, these tests are not written in a programming language but in a shared language that everyone speaks. Test automation engineers then translate into the code under test. Besides, BDD is principally concerned with the results of a high-level scenario, and its goal is to ensure that the output is correct under a given condition.

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The Benefits of TDD and BDD

Both TDD and BDD have their advantages and benefits.

Benefits of TDD

  • Help find bugs and errors quickly
  • Generates faster feedback from technical stakeholders
  • Speeds up fixes
  • Reduces the time required for rework
  • Boosts developers’ productivity
  • Can result in cleaner designs and higher-quality code
  • Helps create extensive, flexible code that’s easy to maintain

Benefits of BDD

  • Requirements can be standardized and defined in non-technical language that all stakeholders can understand
  • Promotes an understanding of how the system should behave from the user’s perspective
  • Illustrates real-world scenarios to clarify requirements
  • Improves collaboration between technical stakeholders (developers and QA) and non-technical stakeholders (users)
  • Reduces the effort required to implement post-deployment fixes

Many Agile teams still use TDD instead of BDD since TDD often results in higher-quality code. However, since BDD improves collaboration among a wider audience, it can result in better specifications and ensure that the maximum number of use cases work at a higher level. This can result in greater confidence in the final application.

Ultimately, neither approach is “better” than the other. So, which side of the TDD vs. BDD debate you fall on would depend on considering all these factors.

In a Nutshell

If you are a software engineer, don’t look at BDD TDD in isolation. Instead, understand the benefits of both approaches, clarify your testing goals, and then choose the approach that suits your project, team, and users better.

Frequently Asked Questions

Is BDD a part of the Agile methodology?

Behavior-driven development (BDD) is an Agile software development methodology. In this method, an application is designed and documented around the behavior a user would expect to experience when interacting with it.

What is the purpose of BDD?

Behavior-driven development (BDD) is a methodology in Agile software development that aims to narrow the communication gaps between team members. This method encourages team collaboration between developers, testers, and business analysts.

Are Cucumber and Selenium the same?

Selenium is a testing framework, while Cucumber is a Behavior Driven Development (BDD) tool. Selenium can work independently of Cucumber. Cucumber depends on Selenium or Appium for step definition.

What are the three phases of BDD?

The three phases of BDD are 1.Discovery phase - This is where the acceptance criteria are researched and decided. 2.Formulation phase - Ensures that the acceptance criteria are confirmed and ready to be applied in real time. 3.Automation phase - automates the process of acceptance tests.



Director, Product Evangelist at ACCELQ.


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