TDD vs BDD Comparison

Tohid haghighi
6 min readFeb 21, 2024

TDD (Test Driven Development) and BDD (Behavior Driven Development) are fairly similar development approaches that both emphasize testing and collaboration, yet have major differences in focus and methodology. Simply put, in TDD, developers test first, then use the test results to guide their development, while in BDD, developers express the system behavior they want to create through Gherkin syntax, then code according to those Gherkin expressions.

From a higher perspective, TDD is more developer-centric, revolving around code correctness, with programming language-specific frameworks. On the other hand, BDD is more user-centric, revolves around system behavior, and promotes collaboration between relevant stakeholders with a domain-specific language.

In this article, we will explore in-depth the differences between TDD vs BDD through true-to-life testing scenarios, and learn about the popular TDD and BDD testing frameworks.

TDD Flow
BDD Flow

For example, below is an example of Gherkin describing the Checkout process:

Feature: Checkout Process

As a customer

I want to be able to add items to my cart and complete the checkout process

So that I can purchase products online

  • Scenario: Add item to cart

Given I am on the product page

When I click on the “Add to Cart” button for product “ABC”

Then the item “ABC” should be added to my cart

  • Scenario: Remove item from cart

Given I have “ABC” item in my cart

When I click on the “Remove” button for item “ABC”

Then the item “ABC” should be removed from my cart

  • Scenario: Update quantity of item in cart

Given I have “XYZ” item with quantity “2” in my cart

When I update the quantity of item “XYZ” to “3”

Then the quantity of item “XYZ” in my cart should be “3”

  • Scenario: Proceed to checkout

Given I have items “ABC” and “XYZ” in my cart

When I click on the “Checkout” button

Then I should be redirected to the checkout page

  • Scenario: Enter shipping details

Given I am on the checkout page

When I enter my shipping information

Then my shipping details should be saved

  • Scenario: Enter payment details

Given I am on the checkout page

When I enter my payment information

Then my payment details should be saved

  • Scenario: Place order

Given I have entered my shipping and payment details

When I click on the “Place Order” button

Then my order should be placed successfully

And I should receive an order confirmation

What’s the Difference?

The primary differences between TDD and BDD lie in what is being tested and how. BDD predominantly focuses on the end user’s standpoint in its testing of the application behavior, whereas TDD focuses on smaller sections of functionality to be tested by itself.

Additionally, BDD involves a larger group of people — project managers, developers, and test engineers who come together to develop the behavior examples. As such, a great deal of communication is needed before anything is implemented. On the other hand, TDD can be done by a sole developer without external input from project managers or stakeholders.

Test-Driven Development (TDD)

  • Implementation of code functionality through a test-first approach
  • Test cases written with programming-centric terminology
  • Collaboration between developers and testers
  • Focuses on low-level unit tests that verify the behavior of individual code units
  • Tests organized based on code structure and hierarchical or modular approach
  • Ensures code correctness through automated tests
  • Tests are written before implementing corresponding code
  • Narrow scope, typically focusing on individual code units
  • Technical and implementation-centric
  • Fine-grained, testing individual code units in isolation
  • Iteratively refines code through test failures and subsequent code modifications

Behavior-Driven Development (BDD)

  • Collaboration, shared understanding, and validation of system behavior from a user’s perspective
  • Scenarios written in a natural language format, easily understood by both technical and non-technical team members
  • Collaboration among developers, testers, and business stakeholders to define and validate system behavior
  • Focuses on higher-level tests that simulate user interactions or end-to-end scenarios
  • Scenarios organized around desired behavior, typically grouped by specific features or functionalities
  • Promotes shared understanding, communication, and validation of system behavior
  • Scenarios are defined collaboratively before implementing the code. Can implement TDD within BDD
  • Broad scope, covering multiple units of code working together
  • User-focused and behavior-centric
  • Coarser-grained, testing system behavior as a whole
  • Iteratively refines scenarios and behavior through collaboration and feedback

What is BDD (Behavior Driven Development)?

Simply put, BDD is an agile testing methodology that uses system behavior to guide the development activities. Instead of starting with a test like in TDD, BDD starts with analyzing the desired behavior that developers want to create. After that, they’ll express the desired behavior using the Gherkin syntax, which consists of Given — When — Then statements. These statements show developers how to develop the code that fulfills the behaviors described.

Apply TDD

TDD can be a standalone or complementary practice to BDD. Now with the Gherkin statements written out, developers can start implementing automated tests based on them. Depending on the programming language or techstack of the company, developers can choose between Cucumber, Behat, SpecFlow as their BDD testing frameworks.

The first test execution is supposed to fail, but it will provide valuable direction to the developers. After developers have implemented the feature, we can run the automated BDD scenarios again to show that the feature is complete. The cycle then repeats until the application is fully developed.

The ingenuity behind BDD is that it translates complex, highly technical jargon from requirements into readable language so that even non-technical professionals can also join hands and contribute to the project. BDD promotes collaboration and reduces misunderstandings.

Popular BDD Frameworks

Cucumber

Cucumber testing is a behavior-driven development (BDD) testing approach that utilizes the Cucumber tool to define, automate, and execute test cases in a format that is easily understandable by both technical and non-technical stakeholders.

In Cucumber testing, test scenarios are written using a natural language format, often employing the Gherkin syntax. This syntax employs keywords like Given, When, and Then to describe the steps of a test case. This allows business analysts and product owners to write test scenarios in a language that aligns with their understanding of the system being tested.

Pros:

  • Provides an intuitive way to express requirements in a human-readable format.
  • Supports multiple programming languages, enhancing flexibility and adoption.
  • Enables code reusability, allowing for the efficient creation of test cases.

Cons:

  • Gherkin-induced complexity can arise.
  • The Given-When-Then framework, while providing clarity, may result in the creation of redundant steps, potentially increasing maintenance efforts.

SpecFlow

SpecFlow is a testing framework that facilitates code development and collaboration among developers. It supports Behaviour Driven Development, making it easier for developers to write and test code.

Pros:

  • Collaboration drives design progress, involving business analysts, designers, programmers, and producers.
  • Low cost of bug fixes due to real-time visibility during development.
  • Living documentation of progress and failures during code writing and testing.

Cons:

  • Unsuitable for short projects due to time-consuming nature and cost.
  • Expensive for beginners in coding.
  • Dependency on all developers for stable use of Behavior Driven Development.
  • Requires continuous effort and frequent stakeholder meetings.

Katalon

Katalon Platform is a comprehensive quality management platform supporting automated test creation, management, maintenance, execution, and reporting for web, API, mobile across a wide variety of environments, all in 1 place, with minimal engineering and programming skill requirements.

For BDD testing, Katalon Studio has a native integration with the Cucumber framework, allowing you to perform UI & API functional automation tests written in BDD Cucumber format. Katalon Studio comes with many features:

  • Quickly create a feature file (i.e. the documentation for system behavior written in Gherkin syntax).
  • Create test cases using built-in keywords, which are basically code snippets for common test scenarios.
  • Group those steps into test suites and collections for easier management.
  • Reuse test cases from previous test runs across multiple environments.
  • Execute feature files.
  • Generate BDD report files.
  • Sharing and collaboration capabilities.

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Tohid haghighi

Full-Stack Developer | C# | .NET Core | Vuejs | TDD | Javascript