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Behavior Driven Development (BDD)

1. Definition

Behavior Driven Development (BDD) is a collaborative software development approach that focuses on defining and validating application behavior using examples written in a business-readable language. BDD bridges the communication gap between business stakeholders, developers, and testers by expressing requirements as executable specifications. In BDD, tests are derived from expected behavior, not from technical implementation.

2. Purpose of BDD

BDD exists to solve common problems in traditional development and testing:

  • Misunderstood requirements
  • Late discovery of defects
  • Poor collaboration between QA, Dev, and Business
  • Test cases written too late or disconnected from requirements

Primary goals:

  • Ensure everyone understands what the system should do
  • Validate behavior before coding starts
  • Use tests as living documentation
  • Reduce rework and defect leakage

3. Core Principle of BDD

“The system should do what the business expects, described using examples.”

BDD emphasizes:

  • Behavior, not features
  • Examples, not assumptions
  • Collaboration, not silos

4. BDD Workflow (Real Project Flow)

  1. Business / Product Owner: Describes business behavior in plain language
  2. Team Discussion (Three Amigos): Business + Developer + Tester discuss scenarios
  3. Examples Are Defined: Scenarios are written using Given–When–Then
  4. Automation Implementation: Developers/testers automate the scenarios
  5. Continuous Validation: Scenarios run as automated tests in CI/CD

This ensures shared understanding before code is written.

5. Given–When–Then Structure

BDD scenarios follow a strict behavioral structure:

  • Given – Initial context or precondition
  • When – Action performed by the user/system
  • Then – Expected outcome

Example (conceptual):

Given the user is logged in
When the user places an order
Then the order should be confirmed

This structure enforces clarity, focus, and consistency.

6. BDD vs Traditional Testing

Aspect Traditional Testing BDD
Requirement format Documents / user stories Executable scenarios
Focus Verifying functionality Validating behavior
Language Technical Business-readable
Timing After development Before & during development
Collaboration QA-driven Team-driven
Documentation Often outdated Always up to date

7. BDD vs TDD vs ATDD

Aspect BDD TDD ATDD
Focus Business behavior Code design Acceptance criteria
Language Business-readable Technical Business + technical
Audience Business, QA, Dev Developers Business & QA
Tooling Cucumber, SpecFlow JUnit, TestNG FitNesse, Cucumber
Outcome Living documentation Clean code Acceptance coverage

8. Role of a Tester in BDD

A tester in BDD acts as:

  • Behavior analyst
  • Example designer
  • Quality advocate

Key responsibilities:

  • Identify business scenarios and edge cases
  • Convert requirements into clear behaviors
  • Ensure scenarios are testable and automation-friendly
  • Prevent UI/implementation leakage into scenarios

9. What BDD Is NOT

BDD is not:

  • Writing Selenium steps in plain English
  • Automating every scenario
  • Replacing test cases with Gherkin blindly
  • A tool-only approach

BDD fails when:

  • Scenarios describe UI actions instead of behavior
  • Business is not involved
  • Scenarios become long and technical

10. Benefits of BDD

  • Clear, unambiguous requirements
  • Early defect detection
  • Strong collaboration across roles
  • Reduced rework and cost
  • Better automation alignment
  • Scenarios double as documentation
  • High confidence in releases

11. Example: Good vs Bad BDD Scenario

Bad (UI-focused):

Given I click on login button
When I enter username and password
Then I click submit

Good (Behavior-focused):

Given the user has valid credentials
When the user logs in
Then the user should see the dashboard

BDD always describes what happens, not how it happens.

12. When to Use BDD

BDD is ideal when:

  • Business rules are complex
  • Multiple teams collaborate
  • Automation is part of the strategy
  • Agile or DevOps environments exist

BDD may not fit well for:

  • Very small utilities
  • Proof-of-concept spikes
  • One-off scripts

13. BDD in Agile Teams

  • BDD scenarios define acceptance criteria
  • Sprint planning uses scenarios
  • Automation runs every sprint
  • Scenarios evolve with features

BDD aligns perfectly with continuous delivery.

14. Interview-Ready Summary

  • BDD is a behavior-focused development approach
  • It uses examples written in business language
  • Encourages collaboration and shared understanding
  • Scenarios become automated tests and documentation
  • Tools like Cucumber help implement BDD, but BDD is a mindset, not a tool