Behavior Driven Development

Definition and methodology

Behavior Driven Developmentalso known as Specification Driven Development, strengthens collaboration in software projects through the documented description of tasks, goals and results of the software in a comprehensible text form. These descriptions later serve as the basis for automated tests. "If-then" sentences are often used to facilitate the transition between technical requirements and the programming language.

A central component of BDD is ongoing communication within the team and with stakeholders, which is supported by concrete examples. These examples are written in the form of scenarios in standardized language such as Gherkin. These scenarios are not only useful as specifications at the beginning, but also serve as the basis for automated tests and as final system documentation. They thus accompany the entire development process as living documentation.

BDD also focuses on the desired behavior of the software from the user's perspective, not just on technical requirements. This approach enables more precise and targeted development, as it is clear at all times which functionalities the software should offer. Development usually takes place in short iterations, with new or modified software components being continuously checked by the tests already defined. This ensures that the software meets the initially defined requirements at all times and is of high quality.

This approach promotes a better understanding of customer requirements and supports continuous communication between the various project participants. Originally developed by Dan North in 2003, the first BDD framework JBehave, which technically supported the methods and principles of BDD, was also created during this process.

Phases of the BDD

The phases of the Behavior Driven Development (BDD) comprise several steps that build on each other and together enable effective software development. The first step is the discovery phase, in which the team develops a common understanding of the desired behavior of the software. This involves team members from different roles working together to develop concrete examples and scenarios. These scenarios are often formulated in Gherkin language, which enables clear and structured formulation.

Test-driven development

In the next phase, test-driven software development (TDD) is used. Here, automated test cases are developed before the actual code. These test cases initially fail (red) because the corresponding software functions do not yet exist. The code is then adapted and developed so that it passes these tests (green). By linking the Gherkin scenarios with the implementations, developers receive a clear guideline for the implementation of the tests and their successful execution.

During this phase, mock objects are often used to test the scenarios before they are fully implemented. Mock objects simulate parts of the software that have not yet been implemented, which enables step-by-step implementation and testing. This approach ensures that the developed software components meet the requirements of the Gherkin scenarios and helps to create a comprehensible and automatically testable software description.

Implementation and techniques

In the implementation of Behavior Driven Development (BDD), the focus is on outside-in software development that focuses on the requirements of clients, end users and other interest groups. The development process begins with a textual description of the desired behavior of the software in the form of case studies. These examples use standardized keywords such as "Given", "When" and "Then" to mark preconditions, external behavior and the desired result. This structure helps to formulate the requirements clearly and comprehensibly and to transfer them later into automated tests.

Automation and mock objects

A central element in the implementation of BDD is the automation of case studies. Mock objects can be used to simulate parts of the software that have not yet been implemented. This makes it possible to test scenarios at an early stage and gradually replace them with actual implementations. The result is a continuously tested and adaptable software description that accompanies the entire development process.

The specific application of BDD tools translates the defined test cases into executable code. These tools ensure that the developed functions are continuously tested and meet the defined requirements. This methodology not only makes development targeted and efficient, but also transparent and comprehensible for all those involved.

Advantages and disadvantages of BDD

Behavior Driven Development (BDD) offers numerous advantages that are particularly beneficial when developing complex software projects. One of the biggest advantages is improved communication and collaboration between all team members and stakeholders. The standardized and comprehensible language in the scenarios helps to avoid misunderstandings and create a common understanding of the requirements. In addition, BDD test cases are flexible and serve as living documentation that can be adapted at any time and reflects the current status of software development.

Further advantages and disadvantages at a glance

Another advantage of BDD lies in its increased focus on the needs of end users. The focus on user-centered scenarios ensures that the software developed meets expectations in terms of user-friendliness and functionality. This approach also makes BDD ideal for beginners, as it offers a clear structure and comprehensible examples that make it easy to get started.

However, BDD also has some disadvantages. One of the challenges is that poorly written specifications can make developers' work more difficult. Careful formulation of scenarios is essential to ensure effective implementation. In addition, the involvement of multiple parties and continuous communication requires more time, which can lengthen development cycles. For existing projects and legacy code, switching to a BDD workflow can involve considerable effort.