Behaviour-Driven Development (BDD)

Overview

Behaviour-Driven Development (BDD) is an agile software development methodology that extends Test-Driven Development (TDD) by emphasizing collaboration between developers, testers, and business stakeholders.

BDD ensures that software development is driven by business requirements written in a human-readable format.

Key Principles of BDD

Collaboration – Encourages communication between developers, testers, and business stakeholders.
Human-Readable Tests – Uses a Given-When-Then format to describe application behaviour.
Automation-Friendly – Can be automated using frameworks like SpecFlow in C#.
Living Documentation – Serves as an ongoing reference for application functionality.

BDD Workflow

BDD follows these steps:

Define Scenarios – Write behaviour specifications using natural language.
Automate Tests – Implement step definitions in a testing framework.
Run & Verify – Execute the tests and ensure that requirements are met.

Example: BDD in C# Using SpecFlow

Step 1: Write a Gherkin Feature File

Gherkin is a structured language used in BDD for writing behaviour scenarios.

Feature: Calculator
  Scenario: Add two numbers
    Given I have entered 2 into the calculator
    And I have entered 3 into the calculator
    When I press add
    Then the result should be 5

Step 2: Implement Step Definitions in C#

Step definitions map the Gherkin steps to C# methods.

using NUnit.Framework;
using TechTalk.SpecFlow;

[Binding]
public class CalculatorSteps
{
    private Calculator _calculator;
    private int _result;

    public CalculatorSteps()
    {
        _calculator = new Calculator();
    }

    [Given("I have entered (.*) into the calculator")]
    public void GivenIHaveEnteredNumberIntoTheCalculator(int number)
    {
        _calculator.EnterNumber(number);
    }

    [When("I press add")]
    public void WhenIPressAdd()
    {
        _result = _calculator.Add();
    }

    [Then("the result should be (.*)")]
    public void ThenTheResultShouldBe(int expected)
    {
        Assert.AreEqual(expected, _result);
    }
}

Step 3: Implement the Application Logic

public class Calculator
{
    private List<int> numbers = new List<int>();

    public void EnterNumber(int number)
    {
        numbers.Add(number);
    }

    public int Add()
    {
        return numbers.Sum();
    }
}

Benefits of BDD

Improves Communication – Business requirements are clearly defined for both technical and non-technical team members.
Ensures Alignment – Focuses on delivering features that meet business goals.
Encourages Reusability – Test scenarios can be reused across different test cases.
Reduces Ambiguity – Ensures that user stories are well-defined and testable.

Alternative Approaches to BDD

1. Test-Driven Development (TDD)

Focus: Writing unit tests before implementation.
Best For: Code-level correctness.
Example: Writing a test first, then implementing code to pass the test.

2. Acceptance Test-Driven Development (ATDD)

Focus: Defining acceptance criteria before development begins.
Best For: Ensuring that requirements are met from a business perspective.

3. Exploratory Testing

Focus: Manually testing applications to discover unknown issues.
Best For: Uncovering usability issues and edge cases.

Conclusion

BDD helps teams develop software based on real business needs by using structured, human-readable test cases.

With SpecFlow in C#, teams can automate these tests while maintaining clarity and collaboration.

Alternative methodologies like TDD, ATDD, and exploratory testing can complement BDD depending on project requirements.