What development approach focuses on delivering expected behavior for testing?

Behavior-driven development (BDD) is a software development approach that emphasizes collaboration between developers, testers, and non-technical stakeholders to define the expected behavior of the software from the user's perspective. This approach integrates testing into the development process by using a shared language that describes the behavior of the application in a way that is understandable to all parties involved, such as business analysts and product owners.

In BDD, scenarios are written in a format that specifies the system's behavior under various conditions, using natural language constructs. This not only aids in clear communication but also ensures that the development team fully understands the requirements before they begin coding. By concentrating on the expected behavior, BDD supports automated testing, as these behaviors can be directly translated into automated test scripts.

The other approaches, while also valuable, do not center specifically on defining and delivering expected user behavior. For instance, feature-driven development focuses on delivering features as the primary unit of deliverable work, model-driven development emphasizes creating models to represent the structure and behavior of the software, and test-driven development is centered around writing tests before the actual code. Each of these has its strengths, but they do not match the specific focus of behavior-driven development on delivering expected behavior directly related to user requirements.