behavior-driven-development

Behavior-Driven Development (BDD) Skill

This skill provides a comprehensive guide to applying Behavior-Driven Development principles to your coding tasks. BDD is not just about tools; it's a methodology for shared understanding and high-quality implementation.

How to Use This Skill

When the user asks for a feature, bug fix, or refactor, apply the following mindset:

1. Understand Behavior First: Do not start coding until you know what the system should do.
2. Define Scenarios: Create or ask for concrete examples (Gherkin) of the expected behavior.
3. Drive Implementation with Tests: Use the Red-Green-Refactor cycle.

Core Concepts

1. The BDD Cycle

The process flows from requirements to code:

• Discovery: Clarify requirements through examples (The "Three Amigos").
• Formulation: Write these examples as specific scenarios (Given/When/Then).
• Automation: Implement using TDD.

See ./references/bdd-best-practices.md for a detailed guide.

2. Writing Scenarios (Gherkin)

Scenarios are your "Executable Specifications".

• Keep them declarative (business focus).
• Avoid technical jargon and UI details.
• One behavior per scenario.
• Use bdd-specs.md as the planning-stage scenario inventory in the superpowers workflow. During brainstorming and plan writing, keep the reviewed Given/When/Then scenarios in docs/plans/.../bdd-specs.md so design review, task decomposition, and sprint contracts all read from the same source.
• Store executable scenarios in .feature files, NOT as code comments - once implementation begins, translate the scenarios that will be automated into .feature files or the framework-native executable test format. bdd-specs.md is for design and planning; .feature files are for automation and living documentation.

See ./references/gherkin-guide.md for syntax and storage structure.

3. Red-Green-Refactor (TDD)

The engine of implementation:

1. RED: Write a failing test for the scenario (or a unit thereof).
2. GREEN: Write the minimal code to pass the test.
3. REFACTOR: Clean up the code while keeping tests passing.

CRITICAL: The Iron Law

"No production code is written without a failing test first."

The Red step MUST verify the test fails for the right reason (run the test and read the failure output) before writing any implementation. Skipping or rationalizing this step produces:

1. Tests that pass spuriously — you cannot tell if they are capable of failing.
2. Implementation-biased tests — they reflect the code that was written, not the behavior under contract.
3. Legacy code from day one — no behavioral safety net catches future regressions.

References

• ./references/bdd-best-practices.md - BDD methodology, discovery, formulation, and automation
• ./references/gherkin-guide.md - Gherkin scenario syntax, storage structure, and examples