Behaviour-Driven Development: Making Tests Everyone Can Read
One of the persistent frustrations in software development is the gap between what the business said it needed and what the development team built. Requirements get interpreted, compressed into tickets, estimated, developed, tested, and delivered — and at some point in that chain, the original intent gets lost. The product owner sees the feature demo and says: "That's not quite what I meant." BDD is an attempt to close that gap by making the specification of expected behaviour explicit, readable, and executable.
What Is BDD?
Behaviour-Driven Development is a software development practice that encourages collaboration between developers, QA engineers, and non-technical stakeholders — product owners, business analysts, end users — to define how software should behave before a line of code is written. The key word is "behaviour": BDD focuses not on how a feature is implemented but on what it should do, expressed in terms that anyone involved in the project can read and verify.
BDD emerged from Test-Driven Development (TDD) — the practice of writing tests before writing code. TDD is valuable but technical: the tests are written in code and are readable primarily by developers. BDD takes the same "test first" principle and expresses it in structured natural language, making it accessible to the whole product team.
The Given-When-Then Format
The lingua franca of BDD is the Given-When-Then format, sometimes called the Gherkin syntax (after the Cucumber testing tool that popularised it). Every scenario is expressed as a three-part structure:
Given: the initial context or state of the system before the action is taken. "Given a registered user is on the checkout page with two items in their cart."
When: the action or event that triggers the behaviour being tested. "When they apply a valid 10% discount code."
Then: the expected outcome — what should be observable after the action. "Then the order total should reflect a 10% reduction and the discount code should be marked as used."
The power of this format is that it is simultaneously a specification, a test case, and — when connected to an automation framework — an executable test. The product owner can read it and confirm it captures the intended behaviour. The developer can use it to guide implementation. The QA engineer can automate it and run it as part of the test suite.
Connecting Acceptance Criteria to Automated Tests
In Scrum, user stories are typically accompanied by acceptance criteria — the conditions that must be satisfied for the story to be considered done. BDD makes acceptance criteria testable by expressing them as Given-When-Then scenarios.
This connection is powerful. Instead of acceptance criteria that are written once, reviewed at the Sprint Review, and then discarded, BDD scenarios become living documentation: they are maintained alongside the code, run with every build, and fail visibly when a change breaks expected behaviour. The test suite becomes a specification that stays current because it is enforced by the build pipeline.
BDD Tooling
Cucumber. The most widely used BDD framework. Supports multiple languages (Java, Ruby, JavaScript, Python). Scenarios are written in Gherkin and connected to step definitions in the implementation language. Has a large ecosystem of integrations with CI/CD pipelines and reporting tools.
Behave. The Python-native BDD framework, following the same Gherkin convention as Cucumber. Clean and lightweight; the natural choice for Python teams.
SpecFlow. The .NET ecosystem's answer to Cucumber. Integrates tightly with Visual Studio and supports C#, F#, and VB.NET. Widely used in enterprise Microsoft-stack environments.
Introducing BDD in a Scrum Team
The entry point for BDD in a Scrum team is the refinement process. Instead of writing acceptance criteria in bullet-point form, the team writes them as Given-When-Then scenarios collaboratively — product owner, developer, and QA in the same room (or the same video call). This practice is sometimes called the "Three Amigos" — three perspectives that reduce the chance of misunderstanding.
The first few attempts will be rough. Writing good BDD scenarios is a skill: scenarios should describe behaviour at the right level of abstraction — not too close to the UI ("When they click the green button"), not too vague ("When they do the checkout thing"). The team gets better at it through practice and through reviewing scenarios together before they are automated.
When BDD Succeeds — and When It Becomes Overhead
BDD works well when the whole team — including the product owner — participates in writing scenarios. When it is used as a collaboration tool, it catches misunderstandings early, produces readable documentation, and gives QA automation a clear specification to implement against.
BDD becomes overhead when it is treated as a QA responsibility rather than a team practice. When developers and product owners hand off requirements to QA engineers to "write the BDD scenarios," the collaboration disappears and you are left with a testing framework that requires extra maintenance. The scenarios drift from the real behaviour of the system. The suite grows large and slow. The team stops trusting it.
The deciding factor is ownership. BDD scenarios that are written collaboratively, reviewed by the product owner, automated promptly, and maintained as a team are a genuine asset. BDD scenarios written by one person in isolation are a maintenance burden. The practice is the collaboration, not just the syntax.
XNM Consulting helps organisations build agile delivery capabilities that connect business intent to working software. Learn more on our Program and Project Delivery page.