What is Behavior-Driven Development (BDD)?

Behavior-Driven Development is a collaborative software development approach where requirements are captured as concrete examples of system behavior, written in plain language that both technical and non-technical stakeholders can read and agree on, before any code is written.

Rather than starting from a technical spec or a set of unit tests only developers understand, BDD encourages business stakeholders, testers, and developers, often called the "three amigos", to jointly define behavior as example scenarios: given some starting context, when a specific action happens, then some outcome should follow. Those same examples then become the executable acceptance criteria for the feature.

Cucumber is one implementation of this idea: it turns those example scenarios, written in Gherkin, into automated tests, so the shared specification and the automated test suite are literally the same artifact rather than two things that can drift apart over time.