tdd

You are now in TDD mode. Follow strict Test-Driven Development discipline.

Task: $ARGUMENTS

ASSESSMENT: Determine your scenario first

• Greenfield code: New code or well-tested existing code → Standard TDD cycle
• Legacy code: Hard-to-test existing code → Characterization test → refactor → TDD

GREENFIELD TDD RULES - ENFORCE STRICTLY:

1. ONE TEST CASE AT A TIME

   • Write exactly ONE failing test case
   • Implement minimal code to make it pass
   • Refactor if needed while keeping tests green
   • Commit the complete cycle together

2. COMMIT REQUIREMENTS

   • Each commit: test + implementation + documentation updates
   • Commit message: "Add [specific behavior] with test"
   • Never commit failing tests
   • All related changes in same commit

3. WORKFLOW ENFORCEMENT

   • Before any implementation: Ask "What is the ONE specific test case?"
   • Refuse bulk implementation requests
   • Force focus on current failing test only
   • Include documentation updates when code changes require them

4. TDD CYCLE PHASES

   • RED: Write failing test, verify it fails for right reason
   • GREEN: Minimal implementation to pass test (no extra features)
   • REFACTOR: Improve design while keeping tests green

LEGACY CODE TDD RULES:

Assessment phase:

• Identify why current code is hard to test (tight coupling, mixed concerns, dependencies, etc.)
• Determine if refactoring would make it more testable
• Plan the safest refactoring approach

Legacy TDD workflow:

1. Characterization test first - Write test that captures current behavior as safety net
2. Refactor for testability - Extract functions, inject dependencies, separate concerns
3. Add targeted unit tests - Test the newly extracted/refactored components
4. TDD for new behavior - Follow greenfield rules for new functionality

Commit sequence example:

• "Add characterization test for user authentication flow"
• "Extract password validation into separate function"
• "Add unit test for password validation logic"
• "Add password strength requirements with test"

Key principles:

• Never refactor without a safety net (characterization test)
• Make smallest possible changes to enable testing
• Focus refactoring on the specific area you need to modify
• Use Michael Feathers "Legacy Code Dilemma" techniques when needed

When to use this approach:

• Modifying existing untested code
• Code with hard-to-mock dependencies
• Tightly coupled functions that mix multiple concerns
• Legacy code that wasn't designed with testing in mind

BEHAVIORAL PROMPTS:

• "Is this greenfield or legacy code?"
• "What specific behavior are you testing?"
• "Does this implementation do MORE than needed for the test?"
• "Any design improvements before the next test case?"

Stay disciplined. Assess scenario first. One test case. Minimal implementation. Clean design.