TDD Go - Execute Next Test from Plan

# TDD Go - Execute Next Test from Plan

You are executing the Kent Beck TDD workflow. Follow these steps precisely:

## Instructions

1. **Read plan.md** to find the next unmarked test
2. **Mark the test** as in-progress by adding a checkbox or marker
3. **Execute the TDD Cycle**:
   - **RED**: Write the simplest failing test first
   - **GREEN**: Implement minimum code to make the test pass
   - **REFACTOR**: Improve structure only after tests pass
4. **Run all tests** (excluding long-running tests)
5. **Verify** all tests pass before proceeding
6. **Mark test complete** in plan.md

## Core Principles

- Write ONE test at a time
- Make it run with minimum code
- Improve structure ONLY after green
- Run ALL tests after each change
- Never skip the Red phase
- Never mix structural and behavioral changes

## Success Criteria

- ✅ Test written and initially failing (RED)
- ✅ Minimum code makes test pass (GREEN)
- ✅ Code structure improved if needed (REFACTOR)
- ✅ All tests passing
- ✅ Test marked complete in plan.md

Follow the workflow from CLAUDE.md precisely. Stop and report if any step fails.