TDD Enforcement: RED-GREEN-REFACTOR
The Iron Law
No production code without a failing test first.
Every line of production code must be justified by a test that failed without it. No exceptions unless explicitly approved by a human.
The Cycle
1. RED -- Write a Failing Test
Write a test for the behavior you need. Run it. It MUST fail. If it passes, your test is wrong or the behavior already exists.
verify-RED: Run test → confirm FAIL
If test passes → STOP. Investigate why.2. GREEN -- Write Minimal Code
Write the minimum production code to make the test pass. Nothing more.
verify-GREEN: Run test → confirm PASS
If test fails → fix production code (not the test)3. REFACTOR -- Clean Up
Improve code structure while keeping tests green. Run tests after every change.
Rationalization Table
Do NOT skip TDD. Every excuse has a counter:
| Excuse | Counter | |--------|---------| | "It's too simple to test" | Simple code has simple tests. Write it in 30 seconds. | | "I'll add tests after" | You won't. And if you do, they'll test your implementation, not your intent. | | "This is just a config change" | Config changes break things. Write a test that loads the config. | | "Tests will slow me down" | Debugging without tests is slower. TDD prevents 80% of debugging. | | "I need to prototype first" | Prototypes become production. Start with a test or get explicit human approval to skip. | | "The existing code has no tests" | Add a test for the behavior you're changing. Don't perpetuate the gap. | | "It's a one-line fix" | One-line fixes cause production outages. A one-line test prevents them. |
Testing Anti-Patterns
- Shotgun debugging: Trying random fixes without understanding the failure. Write a failing test first.
- Test-after rationalization: "I'll test it later" is never later. Test first or never.
- Mocking everything: If you mock the world, you test nothing. Mock boundaries, not internals.
- Testing implementation details: Test behavior (what), not implementation (how). Tests should survive refactoring.
Exceptions
TDD may be skipped ONLY with explicit human approval for:
- Throwaway prototypes (marked as such, with a plan to rewrite with TDD)
- Pure documentation or configuration with no behavioral impact
If in doubt, write the test. It takes less time than debating whether to skip it.