Test Driven Development

BLOCKING GATE: Feature or bug to implement.

1. Write test FIRST - name: test_<component>_<scenario>_<expected>
2. Run test - verify it FAILS with expected error
3. If test passes immediately → delete and rewrite (it proves nothing)

EXIT CRITERIA: Test fails for the right reason.

Phase 2: GREEN - Minimal Implementation

BLOCKING GATE: Failing test from Phase 1.

1. Write simplest code to pass current test only
2. No extra features, no premature optimization
3. Run test - verify PASSES

EXIT CRITERIA: Test passes. Nothing more.

Phase 3: REFACTOR - Clean Up

BLOCKING GATE: Passing test from Phase 2.

1. Improve code quality while keeping tests green
2. Run tests after each change
3. If refactoring breaks tests → revert immediately

EXIT CRITERIA: Code clean, all tests green.

Test Quality Checklist

Every test MUST have:

1. At least one assertion with descriptive failure message
2. Descriptive name: test_<component>_<scenario>_<expected>
3. Independent setup - no test order dependency
4. Deterministic - no random data, real timestamps, network calls

Test behavior, not implementation:

• ✅ Public interfaces, observable outcomes
• ❌ Private methods, internal state

Warning Signs

Methodology failing when:

• Writing code before tests
• Tests passing immediately (no RED phase)
• tdd-guard frequently disabled
• Large commits mixing tests and implementation

Recovery: Delete implementation → Write failing test → Verify fails → Minimal code → Commit together

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