TDD Workflow

A disciplined red → green → refactor loop. One failing test at a time, the minimum code to pass, then refactor under a green bar. This is a methodology skill — follow the loop exactly; do not batch.

When to use

Use when behavior can be expressed as assertions: business logic, parsers, APIs, algorithms, bug fixes (reproduce as a failing test first). Skip for throwaway spikes, pure UI layout, or exploratory prototypes with no maintenance horizon.

The loop

RED — write one failing test

• Pick the smallest unspecified behavior.
• Write one test asserting it. Run it. Confirm it fails for the right reason (assertion failure, not import/syntax error).
• A test that passes immediately, or fails on a typo, is not a red. Fix and re-run.

GREEN — minimum code to pass