tomevault-io Test-Driven Development (TDD)
Overview
Write the test first. Watch it fail. Write minimal code to pass.
Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.
Violating the letter of the rules is violating the spirit of the rules.
The Iron Law
NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST
Write code before the test? Delete it. Start over.
No exceptions:
- Don't keep it as "reference"
- Don't "adapt" it while writing tests
- Don't look at it
- Delete means delete
Red-Green-Refactor
RED — Write Failing Test
Write one minimal test showing what should happen.
- One behavior per test
- Clear name describing the behavior
- Real code, no mocks unless unavoidable
Verify RED — Watch It Fail (MANDATORY)
Run the test. Confirm:
- Test fails (not errors)
- Failure message is expected
- Fails because feature is missing (not typos)
Test passes? You're testing existing behavior. Fix the test.
GREEN — Minimal Code
Write the simplest code to pass the test. Nothing more.
Don't add features, refactor other code, or "improve" beyond the test.
Verify GREEN — Watch It Pass (MANDATORY)
Run the test. Confirm:
- Test passes
- Other tests still pass
- Output is clean (no errors, warnings)
REFACTOR — Clean Up
After green only. Remove duplication, improve names, extract helpers.
Keep tests green. Don't add behavior.
Common Rationalizations
| Excuse | Reality |
|---|---|
| "Too simple to test" | Simple code breaks. Test takes 30 seconds. |
| "I'll test after" | Tests passing immediately prove nothing. |
| "Need to explore first" | Fine. Throw away exploration, start with TDD. |
| "Test hard = design unclear" | Listen to the test. Hard to test = hard to use. |
| "TDD will slow me down" | TDD is faster than debugging. |
| "Already manually tested" | Ad-hoc ≠ systematic. No record, can't re-run. |
| "Deleting X hours is wasteful" | Sunk cost fallacy. Keeping unverified code is debt. |
Red Flags — STOP and Start Over
- Code before test
- Test after implementation
- Test passes immediately
- Can't explain why test failed
- "Just this once"
- "I already manually tested it"
- "This is different because..."
All of these mean: Delete code. Start over with TDD.
Bug Fix Flow
- RED — Write test reproducing the bug
- Verify RED — Watch it fail with the bug symptom
- GREEN — Fix the bug with minimal change
- Verify GREEN — Test passes, all tests pass
- Commit
Never fix bugs without a test.
Verification Checklist
- Every new function has a test
- Watched each test fail before implementing
- Each test failed for expected reason
- Wrote minimal code to pass each test
- All tests pass
- Output is clean
- Edge cases and errors covered
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