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skills/tdd-workflow/SKILL.md

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+# Test-Driven Development (TDD) Best Practices
+
+This skill guides rigorous test-first development following the Red-Green-Refactor cycle.
+
+## When to Use
+
+Activate when:
+- Implementing new features
+- Fixing bugs
+- Refactoring existing code
+- Making any code changes
+
+## TDD Core Principles
+
+### Red-Green-Refactor Cycle
+1. **Red** - Write tests FIRST before implementation
+2. **Green** - Write minimal code to pass tests
+3. **Refactor** - Clean up while keeping tests green
+
+### Test Quality Standards
+
+**Write Tests First:**
+- Tests should be minimal and focused on single behaviors
+- Tests are documentation - they clearly show expected behavior
+- If you can't easily test it, the design is wrong - refactor for testability
+
+**Test Organization:**
+- Use table-driven tests for multiple inputs/scenarios in Go
+- Test file naming: `*_test.go` for unit tests, `e2e_test.go` for integration
+- Always test error cases and edge conditions
+
+**Test Types:**
+- **Unit tests** - Mock external dependencies (network, filesystem, time)
+- **Integration tests** - Validate real component interactions
+- **End-to-end tests** - Cover critical user workflows
+
+### Assertion Libraries
+
+**Go Testing:**
+- Use `testify/require` for assertions that should stop test execution
+- Use `testify/assert` for assertions that should continue test execution
+
+## Design for Testability
+
+✅ **Testable patterns:**
+- Dependency injection
+- Interface-based abstractions
+- Pure functions
+- Isolated side effects
+
+❌ **Hard to test (redesign):**
+- Global state
+- Hidden dependencies
+- Tight coupling
+- Side effects mixed with logic
+
+## TDD Workflow
+
+1. Write failing test(s) embodying acceptance criteria
+2. Run tests - verify they fail for the right reason
+3. Implement minimal code to make tests pass
+4. Run tests - verify they all pass
+5. Refactor for quality while keeping tests green
+6. Repeat
+
+## Quality Gates
+
+Before considering work "done":
+- [ ] All tests pass locally and in CI
+- [ ] Coverage ≥ 90% lines/branches
+- [ ] Error cases are tested
+- [ ] Edge conditions are tested
+- [ ] Tests document expected behavior clearly