Behavior Driven Design

Behavior-Driven Design (BDD) is a collaborative approach where we define what the software should do before writing any code. Instead of starting with technical specifications, BDD focuses on describing the actual behavior users will experience.

Start by being crystal clear on the “what” first, then let that guide the “how”.

Be specific: “When a user enters an incorrect password, display a helpful error message and keep their username filled in.” is far better than: “user-friendly login”. These concrete examples become the foundation for development and testing.

Why BDD Matters

Reduced misunderstandings - Everyone agrees on what “done” looks like before development starts
Better team alignment - Concrete examples replace abstract requirements
Clearer requirements - Vague user stories become specific, testable scenarios
Faster feedback - Problems surface in conversations, not after weeks of development
Confident releases - You know exactly what to test when behavior is defined upfront
Less rework - Code satisfies well-defined behaviors rather than best guesses

The BDD Process

1. Start with the User Goal

Identify what the user is trying to accomplish. Focus on the outcome, not the intermediate steps.

Example: “User wants to access their personal dashboard securely” (not “User clicks login button”)

2. Discover the Happy Path

Map out the ideal scenario with concrete examples and real data.

Example: “Given Sarah has a valid account, when she enters ’sarah@company.com’ and the correct password, then she sees her dashboard with recent projects”

3. Explore What Could Go Wrong

Brainstorm realistic failure scenarios that matter to users.

Example: “Given Sarah enters an incorrect password, when she clicks login, then she sees ‘Login details are incorrect. Please try again’ and her email remains filled in”

4. Write Examples Before Code

Turn scenarios into executable examples using the same language from conversations.

Feature: User Login
  Scenario: Successful login
    Given Sarah has account "sarah@company.com"
    When she enters email and correct password
    Then she sees her personal dashboard

5. Build to Satisfy Examples

Develop incrementally using examples as a checklist. Make each scenario pass before moving to the next.

Key Takeaways

What BDD Really Is

Collaboration first - Conversations between people, not just testing tools
Behavior focus - Define what software should do from the user perspective
Shared understanding - Everyone uses the same concrete examples

Why It Works

Prevents rework - Misunderstandings surface in conversations, not after development
Reduces guesswork - Specific examples eliminate ambiguous requirements
Builds confidence - You know exactly what to build before writing code

Next Steps

Pick one small feature - Don’t transform your entire process at once
Gather your team - Include developer, tester, and stakeholder who understands the customer problem fully
Ask “What should happen when…” - Turn vague requirements into specific scenarios
Write it down - Capture examples in whatever format works
Use examples as checklist - Build incrementally to satisfy each scenario

BDD works because it’s simple: talk about what should happen, write it down with examples, then build exactly that.