Test-Driven Development

Drive implementation through tests using a red-green-refactor loop.

Adapted from Matt Pocock's TDD skill.

Philosophy

Test behavior through public interfaces, not implementation details. Good tests read like specifications for what the system does. They should survive internal refactors because they do not know about private functions, internal collaborators, or storage details.

Prefer integration-style tests that exercise real code paths. Mock only at system boundaries: network calls, databases, file systems, clocks, and third-party services. See mocking.md.

When to Use

Use this skill only when the user asks for: