A discipline an agent applies when adding or changing behavior. Start with a preflight: decide whether TDD adds regression value, then whether the project already has usable test infrastructure for that behavior. Only then enter RED → GREEN → REFACTOR. Synthesized from four public TDD skills (mattpocock, obra/superpowers, NousResearch/hermes-agent, affaan-m/ECC).

Preflight before RED — decide whether the change warrants TDD and whether the affected behavior is testable with the project's existing setup.
Never introduce test infrastructure silently — ask first; if declined, prioritize the current task with direct verification; if approved, present a project-specific engineering plan and wait for confirmation.
Write the test first, watch it fail, write the minimum code to pass, refactor on green.
No production code without a failing test — code written before its test gets deleted.
One behavior per cycle — vertical tracer bullets, never all-tests-then-all-code.
Test observable behavior through the public interface, not implementation details.
A test only counts once you've watched it fail for the right reason.

Pure markdown, language- and framework-agnostic — preflight selects the path; the cycle stays strict once TDD applies.

tdd

Core