1 What is BDD?

Software development is not just coding; it is a continuing conversation among stakeholders, users, and the delivery team. Behavior-Driven Development (BDD) aims to capture that conversation in a precise, testable form that guides building and evolving systems. Emerging from TDD to better align technical practice with business needs, BDD uses illustrative scenarios to bridge intent and implementation, yielding living documentation and faster, more meaningful feedback. The chapter frames three persistent pains—unclear or incomplete requirements, unreliable documentation, and slow, noisy feedback—and positions BDD as the connective tissue that maintains traceability from needs to behavior over time.

BDD drives small increments of value through three complementary practices wrapped around lightweight user stories: discovery, formulation, and automation. In discovery, cross-functional requirement workshops use concrete examples to explore business rules and surface ambiguities early. In formulation, those examples become business-readable scenarios (often Given–When–Then in Gherkin) that precisely specify behavior and can be reviewed by stakeholders. In automation, scenarios are executed as tests that guide implementation; developers iterate red–green–refactor (often via TDD) until scenarios pass, creating living documentation and a rapid, reliable feedback loop at the granularity of requirements.

Success depends on genuine collaboration and shared quality ownership; common pitfalls include “BDD without the business,” automation pursued in isolation, confusing or unreadable scenarios, and brittle, hard-to-maintain automation. Naming debates (BDD, ATDD, Specification by Example) distract from the common techniques, and testers remain essential—especially for exploratory work and domain insight. The recommended path is evolution, not revolution: start by strengthening discovery, then move to formulation and automation; run small experiments, adapt practices to context, measure outcomes, and acknowledge that BDD is neither a free lunch nor a silver bullet. When adopted thoughtfully, it reduces waste, rework, and defects while preserving a durable bridge between stakeholder intent and implemented behavior.

BDD is an agile approach to delivering software that introduces three core practices

The TDD cycle starts by writing a test and seeing it fail (Red). Then we write just enough code to have the test pass (Green). Finally, we refactor the code to improve its structure

The BDD cycle is the outer loop – write a failing scenario, get the scenario to pass, then refactor. We enter the inner, TDD cycle to implement the code needed to move from a failing scenario to a passing scenario.

• Modern software development processes suffer from incomplete requirements, unreliable documentation, and slow feedback.
• Behavior Driven Development (BDD) maintains the connection between the requirements and the software by using examples that describe how the system should behave. These examples are called scenarios when expressed in business language.
• There are many tools that can interpret scenarios and directly execute them as tests of the software being developed.
• Each user story describes several rules. Each rule should be illustrated by one or more scenarios, and each scenario helps us explore our understanding of the rule.
• BDD follows the same Red/Green/Refactor cycle as TDD, but at the level of the scenario. Developers use the TDD cycle when getting a failing scenario to pass.
• BDD does not remove the need for traditional software testing, but it reduces the team’s reliance on it by ensuring that most misunderstandings are dispelled before any code is written.
• By collaborating on the creation of the scenarios, the team creates documentation that can be understood by all stakeholders.
• Scenarios, when run as tests, become living documentation of the software that is being built. Living documentation automatically informs the team when the software implementation diverges from the behavior documented by the scenarios.
• BDD is an agile approach to developing software, consisting of three practices: Discovery, Formulation, and Automation.
• BDD adoption is challenging, but there are techniques that can help an organization succeed.

FAQ