arndvs/tdd

TDD (Red-Green Refactor)

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Scope

Backend code only — API routes, services, utilities, data transformations. Frontend components change too fluidly for TDD. If the task involves UI, use /do-work instead.

Workflow

For each vertical slice, repeat this cycle:

1. Red — Write a failing test

Write ONE test that describes the expected behavior. Run it. It MUST fail. If it passes, the test is not testing anything new — rewrite it.

2. Green — Write minimum code to pass

Implement the minimum code required to make the test pass. No more. Run the test. It MUST pass.

3. Refactor — Clean up while green

Improve the implementation without changing behavior. Run the test after every change — it must stay green. Extract helpers, rename variables, simplify logic.

4. Commit

Once the test is green and the code is clean, commit. One test + its implementation = one commit.

Rules

• ONE test at a time. Do not write a test suite upfront — that's horizontal coding.
• Run the test after EVERY step (red, green, refactor). Never skip a run.
• If combining with tracer bullets: one test per vertical slice, one slice at a time.
• Auto-detect the test runner from the workspace (package.json scripts, pytest, phpunit, etc.).
• If no test runner exists, tell the user and ask how to run tests.