What is Behaviour Driven Development (BDD) Testing?

Behaviour Driven Development (BDD) is a software development process that emerged from test driven development (TDD). BDD combines the general techniques and principles of TDD with ideas from domain driven design and object oriented analysis and design to provide software development and management teams with shared tools and a shared process to collaborate on software development.

What is BDD?

BDD is a collaborative approach to software development that bridges the communication gap between technical and non-technical teams. Rather than simply writing tests, BDD encourages teams to develop features and scenarios together, using examples and simple descriptive language that illustrate the behavior of the application from the user’s perspective.

Some key principles of BDD include:

• Focusing on user behavior and desired outcomes rather than technical details
• Using plain language that can be understood by both technical and non-technical teams
• Working in small, iterative cycles to incrementally deliver value
• Collaborating across teams to build shared understanding
• Developing the minimal necessary features to deliver expected behavior

By encouraging collaboration across roles, BDD aims to facilitate greater shared understanding of the goals and vision for a product. This helps align business stakeholders, users, product managers, developers and testers around what needs to be built and why.

Origins of BDD

BDD has its roots in test-driven development (TDD). While practicing TDD, teams write short automated tests to define code requirements before actually writing the code itself. This ensures the code adheres to what is needed.

However, traditional TDD tests are code-centric and technical in nature. BDD builds on TDD by using simple language to describe behavior from user and business perspectives. It focuses on the why behind requirements, not just the how.

The practices of BDD began to take shape in 2003. BDD was heavily influenced by domain driven design (DDD) and acceptance test driven development (ATDD). DDD provided focus on core domain logic and user side effects, while ATDD contributed with collaboration processes around defining acceptance criteria and scenarios.

Early BDD practice evolved across several languages. Frameworks like JBehave (Java), RSpec (Ruby), and Mocha (JavaScript) emerged to enable test automation. Standard vocabulary was defined through the Gherkin language, allowing business and technical stakeholders to interpret and automate specifications consistently.

The term “behavior driven development” itself was coined by Dan North in technology presentations between 2006 and 2008. BDD has since gained widespread popularity across agile software teams as a solution bridging communication gaps between business experts defining needs and technical teams responsible for implementation.

BDD Vs TDD

While BDD is an extension of TDD, there are some key differences:

• Language – BDD uses simple business-readable language while TDD tests often use technical code-centric language
• Audience – BDD specifications can be written by non-developers but TDD tests usually require programming knowledge
• Scope – BDD features can specify front to back system behavior spanning various components while TDD tests tend to focus on specific class behavior
• Automation – Automating BDD features requires entire infrastructure while TDD tests can individually automation units

So while BDD does not replace TDD, it supplements traditional unit testing methods with high-level automation tied to system requirements written from the user perspective. Together these testing approaches provide comprehensive specification and validation of application behavior at different levels.

Key Benefits

Some of the key benefits provided by BDD include:

• Creating a shared understanding of requirements across teams
• Quickly validating development progress and user value
• Reducing misinterpretations and defects early
• Improving communication between technical and non-technical teams
• Providing better documentation of specifications using concrete examples of behavior
• Increased confidence that the delivered functionality behaves as the business intended
• Promoting good practices like automation, refactoring, and iterative development

By formally capturing requirements as executable specifications understood across teams, BDD ensures quality is built-in to development practices rather than an afterthought. Let’s examine some of the BDD specifics in more detail.

BDD Practices

While BDD principles can be applied regardless of specific tools and frameworks, there are some standard BDD practices:

User Stories

BDD teams often use a technique called User Story Mapping to determine functionality that will offer value to users. User stories capture WHO the user is, WHAT they need to do, and WHY that goal or task is important to them.

Feature Files

Plain language descriptions of software features are written up as “feature files” using a simple domain-specific language called Gherkin Syntax:

Feature: User authenticates to access account

  Scenario: Valid username and password
    Given I am a registered user
    When I enter a valid username and password
    Then I should be authenticated to access my account

Automated Acceptance Tests

The scenarios in feature files act as automated acceptance tests which developers use as specifications for what code they need to write. Tests are run early and often to check and validate that code is delivering expected behavior.

This shared understanding between the tests and code is where BDD gets its name — the tests describe the desired “behavior” that code should demonstrate.

The BDD Cycle

The entire BDD process is driven by repeatable cycles that continuously explore, test, develop, and deliver real working software:

1. Identify user story priority with Product Owner
2. Detail new scenarios and examples through discussion
3. Formally capture details examples as tests
4. Watch tests fail (red)
5. Develop minimal code to pass test (green)
6. Refactor and optimize (refactoring)

This red-green-refactor cycle repeats throughout iterative development, delivering complete thin vertical slices of working features with each cycle.

Why is Behaviour Driven Development So Important?

BDD brings several important benefits that address many problems teams encounter during software development:

Alignment Between Teams

BDD enables far greater alignment across business, development, testing and operations teams by forcing collaboration around concrete examples. These examples illustrate expected behavior from real-world user perspectives.

This prevents misinterpretations of requirements while promoting a shared understanding of what users actually need. Everyone understands the reasoning behind features – the why not just the what.

Understanding

By using consistent terminology understood by all team members, BDD ensures that there is consistent understanding across roles of what needs to be built and why.

Collaboration

Because BDD user stories, scenarios, and features files are written collaboratively, BDD enables better and more frequent communication between team members. Misunderstandings can be cleared up quickly.

Flexibility

Because the primary artifacts of BDD — user stories and features — describe behavior from user and business perspectives, they allow the software architecture to adapt and change more easily over time. The behavior describes WHAT rather than HOW.

Focus on User Value

BDD’s emphasis on illustrating functionality from end user perspectives results in software that actually helps users achieve their goals. This avoids over-engineered solutions that are correct but offer little business value.

By driving discussions and development around real-world scenarios, BDD increases customer and user satisfaction.

Automated Validation

BDD tests describe desired behavior that act as living requirements and specifications, providing constant validation of software correctness as code evolves. Tests catch any regressions quickly.

Confidence

The collaborative nature of BDD features aligned with constant feedback from automated tests enables teams to ensure that they are delivering real user value iteration by iteration. Confidence increases as more features are explored, tested, and successfully developed.

Why Do You Need BDD Testing?

There are some fundamental problems with how software teams traditionally interpret, implement, test, and deliver requirements that BDD testing aims to solve:

• It helps bridge the communication gap between technical and non-technical teams. BDD uses simple language that describes user behavior and requirements, allowing product owners, business analysts, developers, and testers to collaboratively build features.
• BDD focuses on the user’s perspective and the value being offered. Test cases are based on what the user needs to do and what value they should get. This keeps the focus on delivering business value.
• It supports agile development. BDD helps teams iterate faster by establishing evaluation criteria upfront and testing those continually. Issues can be caught early before they become expensive to fix.
• BDD tests are reusable and readable. The test cases serve as system documentation that gets maintained as features evolve. New team members can quickly understand behavior from the BDD tests.
• BDD tests are automated. Automation gives fast feedback on business risks of changes. Tests can be rerun quickly whenever regressions are suspected. This encourages continuous testing.
• BDD enables modeling of complex scenarios. Using explicit contexts and test data, BDD allows testing of edge cases and boundary conditions that are hard to keep track of manually.

So, BDD improves communication, focuses on value, supports agility, provides living documentation, enables automation, and models complex scenarios. Adopting it leads to faster delivery of quality software.

Advantages of BDD Testing

Adopting a BDD approach provides several key advantages:

Improved Collaboration

• Whole team involvement in spec process
• Increased communication across roles
• Shared understanding of goals
• Quick clarification of ambiguities

Better Requirements

• Features describe required behavior simply
• Less misinterpreted specifications
• Focus on the problem, not solution

Rapid Validation

• Automated tests provide rapid feedback
• Confidently evolve code without fear of regression
• Fix defects early while code is pliable

Increased Business Value

• Software delivers real user value quicker
• Tight feedback loops keep priorities aligned
• Minimal features drive development effort

Reduced Defects

• Fewer ambiguities in specifications
• Tests catch defects early in development cycles
• Issues fixed when code is still pliable

Flexible Design

• Specifications describe behavior without assuming solution
• Design can adapt to change more easily over time
• Architectural flexibility enables innovation

What are the Common Challenges of BDD?

While BDD offers many benefits, adopting it also comes with some challenges:

Transition Overhead

Switching established teams to BDD can temporarily reduce velocity due to the learning curve and increased collaboration overhead. Expectations have to be set appropriately.

Specification Effort

Writing features and scenarios well is difficult. It takes practice to specify behavior without ambiguous and inconsistent language.

Test Maintenance

Like any automated test suite, BDD tests require ongoing maintenance as code evolves to keep them passing and relevant.

Over-Specified Systems

It’s easy to over-specify behavior upfront in ambition. Teams must consciously focus features on current priorities.

Finding Examples

Illustrating required behavior with concrete examples that make sense to business experts can sometimes be difficult for technical teams. Real-world usage often has odd edge cases.

Automation Challenges

Automating tests for some behaviors and technologies presents challenges. Teams may need additional tools and infrastructure.

The key to overcoming these challenges lies in starting slowly, learning iteratively, and refining skills with each feature cycle. BDD is as much about mindset shift as it is about tools.

How BDD Testing Works

BDD combines a standardized collaborative process for specification with test automation to drive development:

The BDD Cycle

1. Discuss new user story and clarify goals
2. Identify happy path and edge case scenarios
3. Formally capture details examples as automated tests
4. Watch tests fail (red)
5. Develop minimal code to pass test (green)
6. Refactor and optimize (refactoring)

Key roles collaborate at various points:

• Product Owner: Prioritizes user stories representing business value
• Business Analyst: Provides examples illustrating required real-world behavior
• Developer: Defines formal tests replicating examples and implements code
• Tester: Confirms tests represent requirements and pass as expected

Living Documentation

Formal examples are documented as feature files written in Gherkin syntax:

Feature: User authentication

  Scenario: Valid credentials
    Given I am a registered user
    When I enter a valid username and password 
    Then I should gain access to the system

These act as living specifications that must always pass to confirm the software system does what business experts expect.

Development Standards

Step definitions bind plain text steps to executable test code:

@Given("I am a registered user")
public void registeredUser() {
  // Code to setup user
}

@When("I enter a valid username and password") 
public void validCredentials() {
  // Code to enter credentials  
}

@Then("I should gain access to the system")
public void accessGranted() {
  // Code to check access  
}

These automated checks confirm that the behavior of code matches specifications.

Test Automation Frameworks

Tools like Cucumber, SpecFlow, Behave, and JBehave are often used to automate BDD tests for different languages. These frameworks allow binding Gherkin features to executable step code.

Reporting & Traceability

Test results provide traceability back to original examples and features to showcase progress. Reports confirm which behaviors are working and which are not.

By combining a standardized collaborative process with living documentation and test automation, BDD aligns business and technical understanding of what needs to be delivered.

How Do I Implement BDD?

Follow these best practices when implementing BDD:

Start Small

Introduce BDD slowly into one project area to learn practices and tools incrementally before expanding your initiative. Manage expectations appropriately.

Involve Roles Early

Involve all roles early and continuously, especially product experts and business analysts, to ensure tests reflect real-world needs.

Use Examples

Encourage discussions with examples. Ask business experts for realistic use cases and edge cases that the system must handle. Capture these collaboratively as formal scenarios.

Use Simple Language

Favor simple, clear language over complex terminology in features. These act as requirements — stakeholders should understand them clearly.

Automate Tests Early

Automate tests as early as possible to get rapid feedback on progress. Prioritize test coverage of critical business scenarios.

Run Tests Often

Run tests frequently and fix failures immediately. Scheduling automated test runs gives fast feedback to developers on iterations.

Refactor Mercilessly

Dedicate effort to refactoring code to keep it simple, maintainable, and testable as changes accumulate across iterations. Technical debt accumulates quickly otherwise.

Review Metrics

Review test metrics and traceability regularly to determine areas lacking test coverage or needing better test practices. Use this to continuously improve the testing process.

Adopting these practices helps organizations implement BDD testing effectively to achieve desired benefits like improved shared understanding, rapid validation, and greater user value delivery.

Conclusion

In summary, Behavior Driven Development combines specification by example, living documentation, and test automation to provide several key benefits:

• Improved collaboration and shared understanding across teams
• Less ambiguous requirements that focus on the problem rather than solution details
• Rapid validation of software behavior through automated checks
• Increased confidence that delivered software offers real user value
• Reduced defects by catching issues early while code is still pliable
• More flexible code design that can adapt to changing needs

However, BDD comes with challenges like temporary reductions in velocity, increased specification effort, test maintenance, and example identification.

By implementing BDD testing incrementally and involving all team members actively in the specification and validation process, organizations can overcome these hurdles to realize improved alignment of priorities, faster feedback on progress, and greater user satisfaction.

The collaborative, example-focused process combined with living documentation and test automation makes BDD a very valuable development methodology for teams to consider, especially in complex problem domains.