[Feature]: Add Test-Driven Development (TDD) Support to the Framework #2634

Problem Statement

The framework currently lacks built-in support for Test-Driven Development (TDD). Developers who want to follow TDD practices are frustrated by the absence of structured test scaffolding, spec-first workflows, and testing utilities natively integrated into the framework lifecycle.

Proposed Solution

Integrate TDD support natively into spec-kit by providing:

• A spec-first scaffolding command (e.g. spec-kit tdd init) that generates failing test stubs before implementation
• A built-in test runner hook that enforces the Red-Green-Refactor cycle
• Auto-generation of test skeletons from spec definitions
• Watch mode support for continuous TDD feedback loops
• Clear documentation and examples for TDD workflows within the framework

Alternatives Considered

Using third-party TDD libraries (e.g. Jest, RSpec) independently — but these lack integration with spec-kit's spec lifecycle and require additional configuration overhead.

Component

Specify CLI (initialization, commands)

AI Agent (if applicable)

None

Use Cases

1. When a developer wants to write a failing test before implementing a feature spec
2. During spec review to validate each spec has a corresponding failing test
3. When integrating with CI/CD pipelines that enforce TDD coverage gates

Acceptance Criteria

• spec-kit tdd init command is available and generates failing test stubs from specs
• Red-Green-Refactor cycle is enforced by the framework's test runner
• Watch mode runs tests automatically on file save
• TDD workflow is documented with examples in the official docs
• Existing specs remain unaffected (backwards compatible)

Additional Context

No response