tdd

Topics in the source

• Test-Driven Development
• What a good test is
• Seams: where tests go
• Anti-patterns
• Rules of the loop

TDD is the red → green loop. This skill is the reference that makes that loop produce tests worth keeping: what a good test is, where tests go, the anti-patterns, and the rules of the loop. Every section applies on every cycle: consult them before and during the loop, not after. When exploring the codebase, read GLOSSARY.md (if it exists) so test names and interface vocabulary match the project's domain language, and respect ADRs in the area you're touching. Tests verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't. A good test reads like a specification: "user can checkout with valid cart" tells you exactly what capability exists, and it survives refactors because it doesn't care about internal structure. See tests.md for examples and mocking.md for mocking guidelines. A seam is the public boundary you test at: the interface where you observe behavior without reaching inside. Tests live at seams, never against internals. Test only at pre-agreed seams. Before writing any test, write down the seams under test and confirm them with the user. No test is written at an unconfirmed seam. You can't test everything, so agreeing t

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